Vaccines: A Historical Review About Immunity and Vaccines Against H2N2

 

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Although the exact subtypes that sparked influenza pandemics prior to 1918 remain a bit murky, the ECDC graphic (above) from 2015 suggests an H2N3 pandemic likely emerged in 1889, followed 11 years later by an H3 influenza.

The known history of influenza pandemics going back more than 125 years has been a repeating pattern of H1, H2, and H3 viruses (H2, H3, H1, H2, H3, H1 . . .) prompting the question: `Are Influenza Pandemic Viruses Members Of An Exclusive Club'.

Novel H1, H2, and H3 flu viruses appear to have fewer barriers to overcome in order to jump to humans - and while that doesn't preclude the breakthrough of an H5, H7, or H9 outlier - it suggests we should expect an H2 virus to eventually  return as a pandemic threat.

This is hardly a new idea. 

Fifteen years ago, after the furor over the 2009 H1N1 pandemic had finally died down, some researchers suggested it might make sense to add an H2N2 component to the seasonal vaccine to head off the `next' pandemic (see Nature: A Preemptive H2N2 Vaccine Strike?).

In 2012, in H2N2: What Went Around, Could Come Around Again, we looked at a study conducted by scientists working at St. Jude Children's Research Hospital - published in the Journal of Virology - that concluded that H2N2 could well pose a threat to humanity once again.

A press release on this research warned:

1950s pandemic influenza virus remains a health threat, particularly to those under 50

St. Jude Children's Research Hospital scientists report that avian H2N2 influenza A viruses related to 1957-1958 pandemic infect human cells and spread among ferrets; may aid identification of emerging threats.

And we revisited the topic in 2018, in J.I.D.: Population Serologic Immunity To H2N2 For Pandemic Risk Assessment, which warned: Population immunity to H2 viruses is insufficient to block epidemic spread of H2 virus. An H2N2 pandemic would have lower impact in those born before 1968.

While it doesn't get much press, avian H2N2 (and other H2 subtypes) continue to circulate in the wild. A few we've covered include: 

• In 2019 we looked at Viruses: Molecular Characterization of a Novel Avian Influenza A (H2N9) Strain Isolated from Wild Duck in Korea in 2018
• In 2017, in H2N2: Everything Old Is Flu Again, we saw a study published in The Journal Of Veterinary Medical Science, which detailed the finding of H2N2 in Siberian Muskrats. (see Genetic characterization of an H2N2 influenza virus isolated from a muskrat in Western Siberia).  
• In 2016's A Novel Reassortant H2N8 In China, described an H2N8 avian flu virus was isolated from a domestic duck in Zhejiang Province, Eastern China, in 2013.
• In 2006 and early 2007, a reassorted H2N3 subtype was detected in pigs on two different Missouri farms, which was the first known appearance of an H2 virus in a mammal since it was supplanted by the H3N2 virus in 1968 (see Recently Emerged Swine Influenza A Virus (H2N3) Causes Severe Pneumonia in Cynomolgus Macaques).

All of which brings us to an excellent review article, recently published in the journal Vaccine, which looks at the history of H2N2, and our waning population immunity to this influenza subtype.

Since this is a lengthy, and detailed, review I've simply reposted the link, abstract, and a brief excerpt.  Follow the link to read it in its entirety.  I'll have a brief postscript when you return.

Seven decades after the Asian influenza pandemic: A historical review about immunity and vaccines against H2N2
Alina Tscherne a, Florian Krammer 
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https://doi.org/10.1016/j.vaccine.2026.128467Get rights and content
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Abstract

In 1957, a reassortant influenza A virus (IAV) H2N2 subtype emerged in humans and encountered a population that was antigenically naïve to this subtype. The lack of pre-existing immunity to the H2 hemagglutinin (HA) facilitated efficient human-to-human transmission, and by the end of the Summer of 1957, most countries around the world reported increasing influenza cases caused by the new influenza virus subtype. The pandemic lasted until 1958, resulting in millions of infections globally, with 1–4 million estimated deaths.

The first vaccines targeting specifically the H2N2 subtype were available in autumn 1957, but their limited immunogenicity hampered a successful fight against the “Asian influenza pandemic”. After the pandemic, H2N2 became seasonal in the following years. Most individuals developed immunity against both the H2 HA and N2 neuraminidase (NA) proteins of the virus, and vaccines administered in the early 1960s successfully boosted this immunity. 

In 1968, the circulating H2N2 was replaced by the H3N2 subtype, and individuals with pre-existing N2 immunity were partially cross-protected against severe H3N2 infection, as the two N2 NAs were antigenically similar. Since the disappearance of H2N2 from the human population in 1968, global H2 immunity has been decreasing. 

This raises concerns about a possible re-emergence of the H2 subtype from animal reservoirs, where the virus has circulated for decades, into the human population. As preparedness for future pandemics, research on H2-specific vaccines is currently ongoing, with several candidates being tested in preclinical studies and early-phase clinical trials. In contrast to 1957, vaccine technology platforms, but also the assays used to assess vaccine immunogenicity, and efficacy, have significantly improved.

This review aims to summarize the key historical milestones of the Asian influenza pandemic, the impact of H2N2 immunity during and after the 1957 pandemic, the immunogenicity of H2N2-specific vaccines in both a pandemic and pre-pandemic situation, and H2N2-specific antiviral treatment.

        (SNIP)

       (SNIP)

It has been almost 70 years since the H2N2 pandemic and almost 60 years since the virus disappeared from the human population. The virus is still circulating in the avian reservoir, sometimes close to high-density urban areas like New York City, and the risk for another H2 pandemic has increased, as most of the population is now susceptible to H2.

Although vaccine technologies have improved, inducing strong immune responses to influenza viruses to which individuals are naïve remains challenging as seen with H5N1 and H7N9 vaccines. Furthermore, far less effort is being put into preparing for a potential H2 pandemic than into pandemic preparedness for H5N1. However, the H2N2 subtype has already demonstrated its ability to cause a pandemic, while H5N1 – despite very high prevalence in animals globally – has not yet resulted in a pandemic.

       (Continue . . . )

As the following graphic (from today's review) illustrates, H2N2 emerged after an avian virus (this time H2) reassorted with the existing H1N1 seasonal flu (in an unknown host), and produced a newer, more biologically `fit', virus.

This process was repeated again in 1968 after an avian H3 virus - somewhere in Asia - reassorted with H2N2, producing the H3N2 virus.   While I was only 3 for the H2N2 pandemic - and don't really remember it - I was in high school for H3N2. 

While there are other routes by which an influenza pandemic can emerge, this is the classic scenario, and one that can be repeated at any time with no warning. 

While it is always possible the next influenza pandemic will be an H1Nx, an H3Nx, or something more exotic (H5, H7, H9, etc.); waning population immunity makes an H2Nx virus increasingly likely.  

While we can't know what pathogen will spark the next flu pandemic - or when it will arrive - we can take steps to be better prepared to deal with it.

Assuming, of course, that we can be bothered. 

WHO Influenza at the human-animal interface (March 31st): 13 Novel Flu Infections Detailed

 

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While avian flu reports may seem to have slowed in the first quarter of 2026, we've a new report from the WHO that announces (for the first time I've seen) at least 4 previously undisclosed cases, including a fatal H5N1 case in Bangladesh. 

Today's Influenza at the Human-Animal Interference contains details on:

• 4 - A(H5N1) cases (3 Cambodia*, 1 Bangladesh)
• 5 - H9N2 Cases (4 China, 1 Italy)*
• 1 - H10N3 Case, China
• 1 - H1N1v Case, China
• 1 - H1N2v Case, China
• 1 - H3N2v Case, Brazil

* Note: We've seen another 4 H9N2 cases reported by China & 1 Cambodian H5N1 case since the Mar 31st cutoff

The first, and arguably most significant of these new cases is this previously unannounced case out of Bangladesh:

A(H5N1), Bangladesh

On 9 February 2026, the National International Health Regulations Focal Point of Bangladesh notified WHO of a laboratory-confirmed human case of avian influenza A(H5) infection in a child from Chattogram Division. The patient, with no known comorbidities, developed symptoms on 21 January 2026 and was admitted to hospital on 28 January. A nasopharyngeal swab was collected on 29 January as part of the Hospital-based Influenza Surveillance (HBIS) platform for influenza-like illness (ILI) and severe acute respiratory infection (SARI) sentinel surveillance in Bangladesh. The patient was referred to a specialized private hospital and admitted to intensive care on 31 January.The patient died on 1 February.

On 7 February, the Institute of Epidemiology, Disease Control and Research (IEDCR), serving as the National Influenza Centre (NIC), received and tested the sample, confirming influenza A(H5) by real-time reverse transcription polymerase chain reaction (RT-PCR) on the same day. Virus characterization and whole genome sequencing was conducted at International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b), which confirmed that the A(H5N1) virus belongs to clade 2.3.2.1a of highly pathogenic avian influenza A(H5N1) virus (Gs/GD lineage), similar to the clade of viruses circulating in local poultry since around 2011. 

Genetic sequence data are available in GISAID (EPI_ISL_20367262; submission date 19 Feb 2026; Institute of Epidemiology,Disease Control & Research (IEDCR)).The case had exposure to household poultry, with two ducks and one chicken reportedly dying shortly before the case’s illness onset. Animal and environmental samples were collected and tested with RT-PCR and serology by the zoonotic investigation team of icddr,b. Two samples from ducks in the community and two samples from chicken meat in the freezer of household tested positive for influenza A(H5). Samples from symptomatic close human contacts tested negative for influenza.This is the first confirmed human case of avian influenza A(H5) reported in Bangladesh in 2026.

In 2025, four human cases of avian influenza A(H5) were reported.

This makes the 12th case reported by Bangladesh, and the first fatal outcome.  Today's report also cover the first three Cambodian cases of 2026, which we've previously  discussed (see here, here, and here).

Note: A 4th Cambodian case was announced in April

The report then describes 5 recent H9N2 cases; 4 in China and 1 in Italy (ex-Senegal). 

The two adult cases had underlying conditions. The first two cases had exposure to live bird markets.The last case had exposure to sick poultry. Samples from environments associated with the likely area of exposure of these cases tested positive for A(H9) viruses. The third case likely had exposure to contaminated environments or fomites. No further cases were detected among contacts of these cases.

A(H9N2), Italy, ex-Senegal 

On 21 March 2026, Italy notified WHO of the detection of A(H9N2) virus in an adult male. The case had travelled to Senegal for more than six months and returned to Italy in mid-March 2026. Upon arrival in Italy, the case sought medical care, presenting with fever and persistent cough that had been present since mid-January. Laboratory investigations conducted on a bronchoalveolar lavage specimen on 16 March showed a positive Mycobacterium tuberculosis result, as well as detection of an un-subtypeable influenza A virus. The case was admitted to an isolation room under airborne precautions in a negative-pressure room and received antitubercular and antiviral treatment. As of 24 March, the patient was clinically stable and improving. 

We also get the first details on the Cryptic Announcement of 1 New H10N3 infection last February. 

A(H10N3), China

On 9 February 2026, China notified WHO of one laboratory-confirmed case of human infection with an avian influenza A(H10N3) virus in a 34-year-old man from Guangdong province who developed symptoms on 29 December 2025. On 1 January 2026, he was admitted to hospital and diagnosed with severe pneumonia, severe acute respiratory distress syndrome (ARDS) and sepsis.

Oseltamivir treatment was initiated on 3 January. The patient's condition was stable at the time of reporting. On 12 January, the sample was sent to the provincial laboratory for testing. The result was positive forA(H10N3). On 14 January, the National Influenza Center confirmed the positive result.5 The patient works near two establishments that keep live poultry on the premises and chickens are present at the household.

Environmental samples collected from sites related to likely poultry exposure, including the patient's home, the workplace and a nearby poultry market tested negative for A(H10N3) influenza virus. No further cases were detected among contacts of these cases.A total of 98 close contacts of the patient were traced.Since 2021, a total of seven cases of human avian influenza A(H10N3) virus infection have been reported globally and all were from China

 Lastly, we get two brief descriptions of recent swine variant cases from China, and a more detailed (but belated) report from Brazil.

Swine influenza viruses in humans

Influenza A(H1N1)v, China

On 20 March 2026, China notified WHO of a laboratory-confirmed case of A(H1N1)v influenza virus infection in a child from Yunnan province. The patient had onset of illness on 30 January 2026, was hospitalized on 2 February with pneumonia, and recovered in a few days. The patient had reported exposure to domestic pigs prior to illness onset.

Influenza A(H1N2)v, China 

On 3 February 2026, China notified WHO of a laboratory-confirmed case of A(H1N2)v influenza virus infection in a child from Yunnan province. The patient had onset of mild illness on 20 January 2026, and the infection was laboratory-confirmed on 2 February 2026. The patient had reported exposure to domestic pigs prior to illness onset. This case and the one above are not epidemiologically linked.

 Influenza A(H3N2)v, Brazil

On 26 January 2026, Brazil notified WHO of a laboratory-confirmed case of A(H3N2)v influenza virus infection. On 1 September 2025, a male child residing in the state of Mato Grosso do Sul presented with ILI symptoms and was taken to a health unit on 2 September. The patient had no reported comorbidities or recent travel history and reported being vaccinated against seasonal influenza in the last campaign.

On 9 September, a respiratory sample was collected at the health unit, which is a sentinel unit for ILI. On 12 September, the Central Public Health Laboratory of Mato Grosso do Sul (Lacen/MS) reported that the RT-qPCR test for influenza A virus subtyping amplified the influenza A marker along with the H3 marker, indicating a swine-origin variant of the influenza H3 virus. The sample was sent to the National Influenza Center (NIC) of the Adolfo Lutz Institute, where the A(H3N2)v was confirmed by molecular tests and genomic sequencing. The sequences were entered into GISAID on 1 October. The sample was also shared with the WHO Collaborating Centre at the US Centers for Disease Control and Prevention (CDC), where it was genomically and antigenically characterized.

An epidemiological investigation was conducted, which identified the case as a student at an agricultural school where pigs and laying hens are raised, although the institution's coordinators reported that the students had not had direct contact with pigs recently. It was reported that the case had contact with classmates who presented ILI symptoms during this period. All household contacts were vaccinated against seasonal influenza in the 2025 season, except for the patient's mother. To date, no other human cases of infection with the A(H3N2)v virus have been detected in association with this case.

While avian flu currently has the bulk of our attention, swine variant influenza poses perhaps an even greater pandemic risk. The CDC's IRAT (Influenza Risk Assessment Tool) lists 3 North American swine viruses as having at least some pandemic potential (2 added in 2019).

H1N2 variant [A/California/62/2018] Jul 2019  5.8 5.7 Moderate
H3N2 variant [A/Ohio/13/2017]         Jul 2019  6.6 5.8 Moderate
H3N2 variant [A/Indiana/08/2011]     Dec 2012 6.0 4.5 Moderate

But there is much diversity among swine flu viruses around the globe, with China's EA H1N1 `G4' virus often cited as the biggest pandemic threat. We've also followed repeated spillovers in Brazil, and last year the Eurasian 1C Swine Influenza A Virus was labeled a `high pandemic risk'.

The reality is, surveillance and testing for swine influenza A viruses is notoriously sub-optimal, and many strains circulate under the radar.  

The fact that we are learning nearly 90 days after the fact about a fatal H5N1 case in Bangladesh, and more than 7 months after a novel H3N2 case in Brazil, reminds us that `no news' isn't necessarily `good news'. 

Mpox Clade Ib: 1st Local Transmission in Denmark & Wastewater Detection in Hawaii

 Data WHO SitRep # 64

#19,131

While Mpox is no longer classified as a PHEIC (Public Health Emergency of International Concern) by the WHO - the recently emerged clade Ib continues to make inroads around the globe - and we are watching for further signs of a recombinant strain which has turned up twice; in travelers to the UK and India.

Although it hasn't taken off  the way that clade II did in the spring of 2022, we continue to see scattered reports - such the following one from the San Francisco Health Department - from around the globe.

Health Alert: San Francisco Reports First Clade I Mpox Case 

April 16, 2026
Situational Update

On April 14, 2026, the first clade I mpox case in San Francisco (SF) was confirmed. The case occurred in an unvaccinated adult who was hospitalized and is improving. The individual reported close contact with someone who traveled internationally to an area where clade I mpox is circulating.

Clade I mpox is distinct from clade II mpox. The mpox outbreak in the United States that began in 2022 is due to clade II mpox and has led to 1066 cases in SF as of April 9, 2026. In contrast, an outbreak of clade I mpox in Central and Eastern Africa has been ongoing since 2023, with sporadic travel-associated cases reported in non-endemic countries and increasing reports of locally-acquired clade I mpox in Europe. Over the last two years, 15 clade I mpox cases have been reported in the United States, including 6 in California. Public health officials are monitoring cases to determine if clade I mpox is more severe than clade II mpox in the United States.

Yesterday, Denmark - which announced an imported case a week ago - announced the detection of 3 more cases, including 1 locally acquired infection.

First case of mpox variant infection in Denmark

Last week, the first case of the mpox variant clade 1b was detected in Denmark, and now three more cases have been confirmed. One of the cases was infected in this country, which is the first example of local transmission.

Last edited on April 27, 2026

Statens Serum Institut (SSI) can now confirm that a total of four cases of mpox clade 1b have been detected in Denmark. In one of these cases, the infection occurred here in the capital area, without prior travel abroad.

Preliminary analyses indicate that there are several independent cases of infection with a common geographical origin outside Denmark.

"It is not unexpected that we are now also seeing local infection in Denmark. Experience from other European countries shows that the infection can spread locally once the variant is introduced," says department head Uffe Vest Schneider from SSI and continues:

"At the same time, it is important to emphasize that the course of the disease has so far been mild, and that the overall risk in the population remains low."

Following the situation closely

In the past year, a number of European countries and countries outside Europe have reported cases of mpox clade 1b with local spread of infection.

Those infected in Denmark have so far had mild illness, and the health authorities continue to assess that there is no cause for concern among the population.

The Danish National Board of Health, the Danish Patient Safety Agency and the State Serum Institut are closely monitoring the situation and collaborating with clinical environments and relevant organizations to track down infection, limit further spread and inform relevant target groups.

At the same time, the importance of vaccination and contraception is emphasized in groups where there is an increased risk of infection.

Also yesterday, the State of Hawaii, Department of Health published the following report on the first detection of clade Ib in wastewater on the island of Oahu. 

MPOX DETECTED AT WASTEWATER SAMPLING SITE ON OʻAHU

Posted on Apr 27, 2026 in Newsroom

HONOLULU — The Hawai‘i Department of Health (DOH) is reporting a wastewater sample from O‘ahu that has tested positive for clade I mpox. The sample was collected on April 13, 2026, from a wastewater treatment facility on Joint Base Pearl Harbor Hickam (JBPHH). This is the first time clade I mpox has been detected in wastewater in Hawaiʻi. To date, no clinical case of clade I mpox has been identified in Hawai‘i.

At this time, the risk for the general public is low. The presence of clade I mpox virus in wastewater does not confirm a clinical case or community spread. Instead, it serves as an indicator to be alert for possible mpox cases. People at higher risk of mpox infection should consider being vaccinated with two doses of the JYNNEOS (mpox) vaccine if not already protected.

The JBPHH facility serves not only on-base military housing and facilities, but public sites that receive large numbers of residents and visitors, including the Pearl Harbor National Memorial Museum.

DOH was notified of the initial detection on April 20, 2026, with positive confirmatory results received on April 24, 2026. Subclade analysis was undetermined due to sample degradation. A subsequent sample, collected on April 20 from the same wastewater facility, has tested negative for mpox. Major civilian wastewater facilities on O‘ahu are routinely tested for clade I mpox, and all samples have tested negative as of April 22, 2026.

Clades are genetically distinct groups, or lineages, of a virus that develop as it evolves over time. There are two types of the virus that causes mpox, clade I and clade II. Both types spread the same way and can be prevented using the same methods. A clade II mpox outbreak in the United States that began in 2022 has led to 65 cases in Hawaiʻi as of April 20, 2026. There has been an ongoing outbreak of clade I mpox since 2023 in Central and Eastern Africa, with recent community transmission in Western Europe. To date, clade I cases in the continental U.S. have been among people who had recently traveled to countries with ongoing outbreaks. So far, there has not been sustained transmission of clade I mpox reported in the U.S. Public health officials are monitoring cases to determine if clade I mpox is more severe than clade II mpox in the U.S.

DOH encourages anyone who has recently traveled to an area with active transmission, or who has been in close contact with a symptomatic individual, to monitor their health and consult with a healthcare provider regarding potential risks. People with mpox often get a rash and may have other symptoms like fever, chills and swollen lymph nodes. The rash, which typically begins as bumps and progresses to blisters and pustules, may be located on the hands, feet, chest, face, or mouth, or near the genitals. If you develop symptoms or believe you are at high risk, contact your healthcare provider to discuss testing and vaccination.

(Continue . . . )

Since the eradication of smallpox in the 1970s, there has been a growing belief that poxviruses are a thing of the past; a near-forgotten relic of the 20th century.

But a 2020 report in the Bulletin of the World Health Organization warned that our waning immunity to smallpox puts society at increasing risk of seeing new poxvirus epidemics (see WHO: Modelling Human-to-Human Transmission of Monkeypox).

The emergence and international spread of 2 new Mpox clades (Ib & IIb) since 2020 - and a new recombinant recently reported in Asia - would seem to reinforce that warning.

Some recent blogs on Mpox research include:

Eurosurveillance: Waning Humoral Immunity Following Monkeypox Virus Infection and Vaccination, Canada, 2020 to 2023

The UK Recombinant Mpox Case: Reactions from the UK Science Media Centre

WHO DON: Broader Transmission of Mpox Due to clade Ib MPXV – Global situation

Preprint: A three-dose MVA-BN Mpox Vaccination Series Improves the Quality of Anti-monkeypox Virus Immunity

Parasite Epi & Ctrl: Preliminary Molecular Detection of Influenza RNA in Synanthropic Cockroaches from Shiraz, Iran

Periplaneta americana - Credit Wikipedia

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The notion that insects could act as (likely mechanical) vectors of influenza viruses is not exactly new; nearly 20 years ago we looked at a study (see Detection and isolation of highly pathogenic H5N1 avian influenza A viruses from blow flies collected in the vicinity of an infected poultry farm in Kyoto, Japan, 2004 by Kyoko Sawabe et al.) that found that at least 2 types of flies could carry the H5N1 virus.

While these flies weren't believed infected with the virus, they could ingest (and subsequently regurgitate or defecate) infected material, or potentially spread it mechanically by their feet or body, thereby spreading the disease.

Four years later Dr. Sawabe and his team would publish (Blow Flies Were One of the Possible Candidates for Transmission of Highly Pathogenic H5N1 Avian Influenza Virus during the 2004 Outbreaks in Japan) where they conclude:

We have suggested here that blow flies are likely candidates for mechanical transmission of HPAI because of their ecological and physiological characteristics as reviewed here. In fact, blow flies have already been recognized as important vectors for mechanical transmission of several serious infectious diseases, that is, poxvirus [28], rabbit hemorrhagic disease [29], and paratuberculosis [30]. Recently, it has been reported that the H5N1 viral gene was detected in house flies [31] and engorged mosquitoes [32]. 

While the `flies as potential vectors of H5N1' would come up occasionally, in 2024 we looked at a new study (Blowflies are potential vector for avian influenza virus at enzootic area in Japan) which warned: 

` . . . C. nigribarbis may acquire the HPAI virus from deceased wild birds directly or from fecal materials from infected birds, highlighting the need to add blowflies as a target of HPAI vector control.'

Six months ago we looked at two more studies;  Nature Sci Rpts: Detection of H5N1 HPAI virus RNA in filth flies collected from California farms in 2024, along with a fascinating study on HPAI carriage by arachnids (see Preprint: Detection and Isolation of H5N1 clade 2.3.4.4b HPAI Virus from Ticks (Ornithodoros maritimus). 

While none of these studies provide smoking guns on the actual spread of a viable influenza virus, they lay out a plausible mechanism for transmission.

All of which brings us to a new study - this time on cockroaches - which finds similar evidence of influenza virus carriage, although the evidence presented isn't  quite as robust (or compelling) as the more extensive research on flies. 

Once again, all testing was done by RT-PCR (targeting the Matrix Gene of influenza A & B), which cannot tell us if the virus was viable (infectious) or its subtype.  

First the link, abstract, and some excerpts from today's study, after which I'll return with a bit more.

Preliminary molecular detection of influenza RNA in synanthropic cockroaches from shiraz, Iran

Mohsen Kalantari a 1, Mozaffar Vahedi a 1, Marzieh Jamalidoust b, Maryam Motevasel c, Amin Hosseinpour  
 https://doi.org/10.1016/j.parepi.2026.e00498Get rights and content
Under a Creative Commons license
 
Highlights

• First molecular detection of Influenza virus RNA in Iranian cockroaches.
• Viral RNA found on cockroach exteriors and inside their digestive tracts.
• Both Influenza A and B RNAs were detected.
• Low detection rate (1.86%) of influenza virus RNA in cockroaches suggests mechanical carriage may be sporadic
• It needs more studies to confirm the presence of viable and infectious of influenza virus in cockroaches.

Abstract

Cockroaches are recognized as significant mechanical vectors for a wide spectrum of pathogens, posing a considerable public health risk. Their habitation in unsanitary environments and promiscuous feeding habits allow them to acquire and disseminate bacterial agents, viruses—including poliovirus and influenza—and protozoan parasites such as Microsporidia and Giardia, as well as the eggs of parasitic worms. This study investigates the potential of cockroaches to mechanically carry influenza viruses, a subject that remains underexplored despite the significant global burden of influenza. 

During the seasonal peak of influenza activity, a total of 322 cockroaches were collected from various high-risk locations in Shiraz, Iran, including hospital premises, university dormitories, and academic faculties. The sampling targeted two predominant species, Blattella germanica and Periplaneta americana, captured from diverse microhabitats such as kitchens, rooms, and sewers. 

Using a highly sensitive real-time PCR methodology, which targeted the conserved matrix genes of influenza A and B viruses, both external body surface washes and internal digestive tract samples were analyzed. The results confirmed the presence of influenza A virus RNA in four external surface samples of Blattella germanica and in two internal digestive tract samples of Periplaneta americana. 

Notably, the majority of positive samples (5 out of 6) were for influenza type A, with one sample positive for influenza type B. The overall detection rate was low (1.86%, 6/322), these findings demonstrate that cockroaches in urban environments can indeed harbor influenza virus RNA, either externally on their bodies or internally within their digestive systems. This molecular detection highlights the presence of viral RNA, suggesting possible mechanical carriage.

However, the detection of RNA alone does not confirm the presence of viable, infectious virus, which is a key limitation of this study. Given their intimate association with human dwellings and food sources, this molecular evidence indicates potential but unconfirmed route for mechanical carriage that warrants further investigation. Crucially, our study design cannot assess transmission risk. Consequently, the findings underscore the necessity for additional comprehensive studies to assess viral viability and to elucidate the potential, yet unproven, role of cockroaches in the epidemiology of influenza.

       (SNIP)

5. Conclusion

This preliminary study provides the first molecular evidence of influenza A virus RNA associated with cockroaches in Iran. The detection of viral RNA on external surfaces and within the digestive tract provides molecular evidence of environmental contamination and ingestion, respectively. The detection of viral RNA on external surfaces and within the gut suggests environmental contamination and passive ingestion, respectively. However, the low prevalence rate (1.86%) indicates that such detections may be infrequent under the studied conditions.

 
The central limitation is that our PCR-based method cannot confirm viral viability or infectiousness, and no such assessments were performed. Therefore, the detection of RNA does not constitute evidence of transmission risk. The critical question of whether cockroaches can carry and transmit viable influenza virus remains unanswered, as our PCR-based method cannot confirm viability nor, without sequencing, provide definitive proof of target origin. Our findings should not be interpreted as demonstrating a transmission pathway but rather as identifying the presence of viral genetic material in an environmental context that justifies further investigation under a One Health framework. Future studies must include viral culture and infectivity assays to move from molecular detection to a substantive understanding of any potential epidemiological role.

          (Continue. . . .)

In addition to flies, beetles (aka Alphitobius diaperinus) and cockroaches can be frequently seen in and around poultry farms, and all three have a reputation for carrying pathogens.  

While evidence for transmission remains elusive, it is worth pursuing.  

We've also looked at a number of other `less obvious' ways the HPAI H5 virus may be spreading.

• We've seen evidence that HPAI may be spread via `contaminated dust particles' - carried by the wind - from one farm to the next (see Preprint: Genetic & Meteorological Data Supporting Windborne Transmission of HPAI H5N1).

• The role of peridomestic mammals - particularly in and around farms - in the spread of HPAI is only partially understood, and remains under-researched (see Emer. Microbe & Inf.: HPAI Virus H5N1 clade 2.3.4.4b in Wild Rats in Egypt during 2023).

How much insects, windborne `poultry dust', or peridomestic rodents contribute to the spread of HPAI is unknown. But given the stakes, these are risk factors that could be better controlled, and that makes research like today's worthy of our attention.  

SCAI 2026 Conference Report: COVID-19 and Severe Heart Attack Increase Mortality by 25% After One Year

ST Elevation Anterior leads 

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In the opening days of the COVID pandemic - long before the first COVID vaccine was produced - we were already seeing evidence of the impact of acute SARS-CoV-2 infection on the cardiovascular system.

In early April 2020, the New York Fire Department reported a 400% increase in sudden cardiac arrest death calls beginning in late March (see NBC affiliate Massive Spike in NYC ‘Cardiac Arrest’ Deaths Seen as Sign of COVID-19 Under counting).

While most of these cases were never tested for COVID-19, this trend became so pronounced that the city ordered new Standards Of Care During A Pandemic: CPR & Cardiac Arrest, limiting the use of CPR in the field.

The following June, JAMA published an original investigation which found a huge increase in out-of-hospital cardiac arrests in New York City during the peak of their COVID-19 epidemic, writing:

From March 1 to April 25, 2020, New York City, New York (NYC), reported 17 118 COVID-19–related deaths. On April 6, 2020, out-of-hospital cardiac arrests peaked at 305 cases, nearly a 10-fold increase from the prior year.

While many of these cases already had underlying cardiac problems, COVID-19 appears to have a direct, and often serious impact on cardiac function.  Over the past 5 years, we've looked at a great many confirmatory studies, including:

The Lancet: Long COVID and Risk of Incident Cardiovascular Disease

EHJ: Accelerated Vascular Ageing After COVID-19 Infection: The CARTESIAN Study

European Society of Cardiology: Major Consensus Statement Released on Long-Term Cardiovascular Impact of COVID Infection

NIH: Study Shows SARS-CoV-2 Infects Coronary Arteries, Increases Plaque Inflammation

Nature: Long-term Cardiovascular Outcomes of COVID-19

While COVID appears to produce a wide range of impacts on our cardiovascular system, the most severe and immediately life threatening is the STEMI (ST Elevated Myocardial Infarction).

These are serious heart attacks that can affect a large portion of cardiac muscle and typically show up on EKGs with Elevated ST wave. In hospital mortality generally runs about 5% to 6%.

Today we've a press release, and a link to a summary, on a paper delivered on Friday (April 24th) at the SCAI Scientific Sessions 2026 & CAIC-ACCI Summit in Montreal, on the long-term impact of COVID on STEMI patients (in hospital, and 1 year after discharge).

Using data from the North American COVID-19 Myocardial Infarction (NACMI) registry - which has previously been used to quantify both in-hospital impact of COVID on STEMI patients, and improvements in 2021 with the release of the vaccine (see NACMI: In-Hospital Mortality Rate in STEMI Patients With COVID-19 Dropped in 2021) - the authors report:

This study found patients with COVID-19 and STEMI had a 67% higher one-year mortality rate compared to patients who did not have COVID-19 (45% vs. 27%, respectively) (p<0.001). 

While most of this increase (86%) occurred in-hospital - some of which may be attributed to the strained healthcare delivery system during the height of the pandemic - this increased mortality continued after discharge.  

Since conference summary is copyrighted, I've just posted the press release.  You'll find a link to the brief summary near the bottom. 

COVID-19 and severe heart attack increase mortality by 25% after one year, more than double pre-pandemic rates

New data from large North American registry points to troubling long-term trend after initial hospitalization

Society for Cardiovascular Angiography and Interventions
SCAI Scientific Sessions 2026 & CAIC-ACCI Summit

MONTREAL – April 24, 2026 – Findings from the North American COVID-19 Myocardial Infarction (NACMI) registry demonstrate significantly higher one-year mortality rates in patients with COVID-19 and ST-elevation myocardial infarction (STEMI) compared to patients with STEMI alone. This registry is the first study to describe long-term outcomes in patients with STEMI and COVID-19. Researchers presented the late-breaking data today at the Society for Cardiovascular Angiography & Interventions (SCAI) 2026 Scientific Sessions & Canadian Association of Interventional Cardiology/Association Canadienne de cardiologie d’intervention (CAIC-ACCI) Summit in Montreal.

COVID-19 can significantly worsen cardiovascular outcomes, placing patients with preexisting heart conditions at increased risk for complications, underscoring the need for heightened clinical vigilance during and after hospitalization. For example, patients who experience COVID-19 and STEMI, a severe type of heart attack caused by a complete blockage of a coronary artery, are seven times more likely to experience in-hospital death, stroke, recurrent myocardial infarction, or repeat unplanned revascularization, compared to those who did not have COVID-19. However, the long-term effects of COVID-19 on this patient population are unknown.

SCAI and the Canadian Association of Interventional Cardiology (CAIC), in conjunction with the American College of Cardiology Interventional Council, collaborated to create the multi-center observational registry, NACMI. NACMI is a prospective, investigator-initiated, multicenter, observational registry of hospitalized STEMI patients with confirmed or suspected COVID-19 infection in North America. This long-term follow-up sub-study included a total of 2,358 STEMI patients, with three subgroups: COVID-19 positive (n=623), COVID-19 negative (n=694), and matched controls (n=1,041).

This study found patients with COVID-19 and STEMI had a 67% higher one-year mortality rate compared to patients who did not have COVID-19 (45% vs. 27%, respectively) (p<0.001). Most deaths (86%) occurred during the initial hospital stay. Among survivors of initial hospitalization, one-year mortality rates were 25% higher in patients with COVID-19 (12% vs. 9.6%) (p<0.001) and more than double the pre-pandemic rate (5.3%) (p<0.001).

“Our findings emphasize that patients who survive a STEMI need close, ongoing attention from their care team, especially when experiencing COVID-19,” said Payam Dehghani, MD, FSCAI, interventional cardiologist at Prairie Vascular Research Inc in Regina, Saskatchewan, Canada. “By partnering with CAIC, we were able to answer this critical clinical question around the long-term outcomes of COVID-19 and STEMI. Clinicians should carefully assess and monitor cardiovascular risk factors, including lifestyle choices, and patients must remain actively engaged in their recovery and follow-up care.”

The researchers note that additional analyses exploring potential gender disparities among patients with COVID-19 and STEMI are underway.

Session Details:

“North American COVID-19 Myocardial Infarction (NACMI) Registry: One-Year Follow-Up”

Friday, April 24; 4:09-4:17 PM ET
Palais des Congrès de Montréal, 510b (5th Level)

Preprint: The Evolution and Transmission Dynamics of H3N2 Influenza Virus Identified in A Respiratory Disease Outbreak in Companion Dogs in Alabama, USA

 

#19,129

Twenty years ago most veterinarians would have told you that dogs were not particularly susceptible to influenza A viruses, but that notion changed in 2004 when we saw the jump of equine H3N8-like influenza to Florida greyhounds.

In 2008, an EID Journal article reported:

Influenza A Virus (H3N8) in Dogs with Respiratory Disease, Florida
Sunchai Payungporn*, P. Cynda Crawford†, Theodore S. Kouo*, Li-mei Chen*, Justine Pompey*, William L. Castleman†, Edward J. Dubovi‡, Jacqueline M. Katz*, and Ruben O. Donis*

Abstract

In 2004, canine influenza virus subtype H3N8 emerged in greyhounds in the United States. Subsequent serologic evidence indicated virus circulation in dog breeds other than greyhounds, but the virus had not been isolated from affected animals. In 2005, we conducted virologic investigation of 7 nongreyhound dogs that died from respiratory disease in Florida and isolated influenza subtype H3N8 virus.

Like its equine counterpart (which has been around at least a half century) - canine H3N8 has not been shown to infect humans. The CDC considered this to be a dog-specific lineage of H3N8; worth watching but not an imminent threat.

In 2007 we saw an avian H3N2 virus jump to dogs in South Korea (see 2008 EID report Transmission of Avian Influenza Virus (H3N2) to Dogs). Analysis showed that the HA and NA genes of the A/canine/Korea/01/2007 (H3N2) isolate were closely related to those identified in 2003 from chickens and doves in South Korea.

Unlike canine H3N8 - which has remained relatively stable - H3N2 has shown an affinity to reassort with other influenza viruses. We've seen numerous reports coming out of both China and Korea suggesting canine H3N2 may be adapting to other hosts, and continues to reassort with other avian and human flu viruses. A few examples include:

A Canine H3N2 Virus With PA Gene From Avian H9N2 - Korea

Canine H3N2 Reassortant With pH1N1 Matrix Gene

Virology J: Human-like H3N2 Influenza Viruses In Dogs - Guangxi, China

Interspecies Transmission Of Canine H3N2 In The Laboratory

In 2015 this Asian canine H3N2 virus finally turned up in North America (see CDC Statement On H3N2 Canine Influenza In Chicago Region), and since then has spread across much of the United States. 

While quantified as a relatively low-risk virus, in 2017 the CDC added Canine H3N2 to their IRAT (Influenza Risk Assessment Tool) listing of novel flu subtypes/strains that circulate in non-human hosts and are believed to possess some degree of zoonotic potential. Their evaluation reads:

H3N2: [A/canine/Illinois/12191/2015]
The H3N2 canine influenza virus is an avian flu virus that adapted to infect dogs. This virus is different from human seasonal H3N2 viruses. Canine influenza A H3N2 virus was first detected in dogs in South Korea in 2007 and has since been reported in China and Thailand. It was first detected in dogs in the United States in April 2015. H3N2 canine influenza has reportedly infected some cats as well as dogs. There have been no reports of human cases.

Summary:  The average summary risk score for the virus to achieve sustained human-to-human transmission was low risk (less than 4). The average summary risk score for the virus to significantly impact public health if it were to achieve sustained human-to-human transmission was in the low risk range (less than 4).

Over the past decade we've looked at a number of studies which have investigated the zoonotic potential of canine H3N2 (see 2017's J. Virology: Zoonotic Risk, Pathogenesis, and Transmission of Canine H3N2), and Frontiers in Microb.: Emergence & Evolution of A Novel Canine-Avian Reassortant H3N2 (China).

Last year (2025) waw two concerning reports come out of China:

Preprint: Fatal infection of a novel canine/human reassortant H3N2 influenza A virus in the zoo-housed golden monkeys

Frontiers Vet. Sci: Genetic Characterization of an H3N2 Canine Influenza Virus Strain in China in 2023—Acquisition of Novel Human-like Amino Acid Substitutions

Although we've yet to see any evidence of human infection with canine H3N2, this virus continues to reassort and evolve, and we've evidence of spillover to felines, primates, and even spillback into birds. 

While most of the research we've seen has come out of Asia, today we've a preprint on the detection of  a new (reassorted) strain of Canine H3N2 in Alabama in 2022. 

First, a link and some excerpts, after which I'll have a brief postscript.

The Evolution and Transmission Dynamics of H3N2 Influenza Virus Identified in A Respiratory Disease Outbreak in Companion Dogs in Alabama, USA

Shakiba Kazemian, Sana Tamim, Peter Neasham, Samiah Kanwar, Kevin Zhong, and 7 more

This is a preprint; it has not been peer reviewed by a journal.
https://doi.org/10.21203/rs.3.rs-9053609/v1
This work is licensed under a CC BY 4.0 License

        PDF  

Abstract

Canine Influenza Virus H3N2, initially of avian origin, emerged in Asia around 2005–2007 and subsequently spread globally, reaching the United States in 2015. Despite initial containment efforts, H3N2 CIV re-emerged in several US states in 2023. This study investigates the evolution and transmission dynamics of H3N2 CIV identified in companion dogs during an outbreak in Alabama, USA, between August and October 2022. 

We performed whole-genome sequencing on five H3N2 CIV isolates and conducted phylodynamic modeling, incorporating 100 global H3N2 CIV genomes per segment. Phylogenetic reconstruction showed the Alabama strains formed distinct, tightly clustered groups, suggesting recent common ancestry and localized evolution. Phylogeographic inference revealed discordant origins for different gene segments. The HA, MP, NP, NS, and PA genes traced ancestry to California strains, the NA gene to Florida strains, and the PB1 and PB2 genes to Illinois strains. 

This genomic incongruence strongly indicates that the Alabama outbreak strain emerged through a reassortment event involving viruses from these three geographically distinct regions.

The findings highlight reassortment as a crucial mechanism driving CIV H3N2 evolution and spread, likely facilitated by the movement of infected dogs. Low canine vaccination requires continued surveillance and shelter-focused vaccination to control CIV outbreaks and monitor adaptation.

       (SNIP)

The findings presented here highlight the importance of continued surveillance for CIV, particularly in settings where dogs interact (dog parks) or are housed in close proximity,such as shelters and breeding facilities, which poses vulnerability for dog populations.Shelters and stray dog populations are a particular challenge since densely populated environments and frequent dog-to-dog contact can act as hotspots for viral transmission and potentially facilitate further reassortment events and contribute to the ongoing adaptation and evolution of the virus.

Our study primarily focused on the genetic analysis of the viral strains circulating during the Alabama outbreak. Future investigations could benefit from incorporating additional data sources and information on dog movement patterns, to provide a more comprehensive understanding of the outbreak dynamics. The introduction of influenza strains from geographically distinct locations coupled with the lack of widespread vaccination in the canine population, created conditions conducive to reassortment and generation of new viral diversity.

In conclusion, the findings from the Alabama H3N2 CIV outbreak strongly suggest that reassortment events play a critical role in the emergence and spread of the virus. This case study underscores the importance of continued vaccination and surveillance for influenza virus evolution in canines and the potential public health implications of reassortment events in zoonotic influenza viruses.

       (Continue . . . ) 

While exact numbers are hard to come by, veterinarians report that uptake of canine flu vaccination remains low. Not all that surprising, given that CIV is not considered a `core antigen', the hassle/expense of scheduling 2 vet visits, and the public's growing distrust of vaccines. 

But companion animals (mostly dogs and cats) are uniquely positioned to serve as a bridge to introduce zoonotic diseases to humans.

Which makes it important that we increase surveillance, and take reasonable steps - where possible - to limit the spread of emerging pathogens, including canine influenza.