EID Journal: Characteristics and Superspreading Potential of Andes Virus Person-to-Person Transmission

R0 (pronounced R-nought) or Basic Reproduction Number.

Essentially, the number of new cases in a susceptible population
likely to arise from a single infection. With an R0 below 1.0, a virus
(as an outbreak) begins to sputter and dies out. Above 1.0, and
an outbreak can have `legs’.

Rt represents the actual transmission of a disease in a population
where some people may be immune and control measures are in place

 #19,334

Four months ago the big infectious disease story was an unusual outbreak of Andes Hantavirus (ANDV) aboard a cruise ship out of Argentina, which resulted in 13 identified cases (12 laboratory-confirmed and 1 probable) and 3 fatalities.

The incubation period for ANDV can run up to 6 weeks, with a 42-day monitoring period generally recommended. Some cases can be mild, or even asymptomatic, but the CFR (case fatality rate) can reach 30%-60%.

Although outbreaks of ANDV are fairly rare, and generally limited in size, we've followed several outliers over the years. 

Including, most famously, a 2019 outbreak in Argentina - where, over a period of 3 months - a total of 34 laboratory-confirmed cases of Hanta Pulmonary Syndrome (HPS) - including 11 deaths - were reported in Epuyén, Chubut Province.

The WHO DON report stated:

The index case had environmental exposure prior to symptom onset on 2 November, and subsequently attended a party on 3 November. Six cases who also attended the party experienced the onset of symptoms between 20-27 November 2018.

An additional 17 cases, all of whom were epidemiologically-linked to previously confirmed cases, experienced symptom onset between 7 December 2018 and 3 January 2019 (Figure 1). Potential human-to-human transmission is currently under investigation.

Following the above outbreak, the NEJM published “Super-Spreaders” and Person-to-Person Transmission of Andes Virus in Argentina, which warned: ANDV Epuyén/18−19 strain shows a facility (R>2) for sustaining continuous chains of transmission if no control measures are enforced. 

The idea that 20% of those infected may be responsible for 80% of the forward transmission of a virus has been around for decades, but gained momentum after the 2003 SARS outbreak. 

During that first SARS outbreak, studies found most patients would typically only infect 1 or perhaps 2 additional people, and often none at all. 

But a small percentage of patients proved unusually efficient at spreading the virus, with some responsible for 10 or more secondary infections (see MMWR Severe Acute Respiratory Syndrome --- Singapore, 2003).

A decade later, we'd see the same phenomenon repeated with MERS-CoV (see Superspreaders & The Korean MERS Epidemiological Report) where one Korean MERS patient (#14) is believed to have infected as many as 85 people, while two others (#1 & #16) appear to have infected more than 50 others between them.

 

According to Stein’s excellent 2011 review Super-spreaders in infectious diseases: 

Super-spreading events are shaped by host, pathogen, and environmental factors. Often, more than one factor may be implicated in the same outbreak.

Superspreading events aren’t limited to coronaviruses, as they have been documented with measles, HIV, TB, S. aureus, Ebola, and various STDs . . .among others (cite) 

In January of 2013, in Influenza Transmission, PPEs & `Super Emitters’ we looked at research that found five patients (19 percent) in their study were "super-emitters" who emitted up to 32 times more flu virus than did the rest. Patients who emitted a higher concentration of influenza virus also reported greater severity of illness.  

While the host and the pathogen are important parts to the equation, environment and opportunity also play a pivotal role in exacerbating these superspreader events.

All of which brings us to an EID Journal Dispatch which finds that the 20/80 rule also applies across a larger sampling of ANDV clusters reported over the years, and while the pooled average Rt remains at a reassuring .74, in some outbreaks (including the NEJM report) that number approached or exceeded 1.0. 

I've only reproduced the Abstract and a few excerpts from the dispatch, so you'll want to follow the link to read it in its entirety.  I'll have a brief postscript when you return.

Dispatch
Characteristics and Superspreading Potential of Andes Virus Person-to-Person Transmission

Zihao Guo1 , Kailun Pan1, Yu Zhao, Sheikh Taslim Ali, Kai Wang, Lirong Cao, Zhuang Cui, Shengqiang Liu, Ka Chun Chong, Daihai He, Shi Zhao , and Yuantao Hao2

Abstract

By using historical contact tracing data, we estimated that 23.4% of case-patients caused 80% of Andes virus (ANDV) person-to-person transmission. We demonstrated a low but nonnegligible probability of observing a large-scale ANDV infection outbreak in a rodent-free setting consisting of close contacts, despite the historically self-limited person-to-person transmission of ANDV.

(SNIP)

On May 2, 2026, an ANDV outbreak aboard the MV Hondius cruise ship was reported to the World Health Organization (WHO), with the first case illness onset on April 3 (10). Subsequent epidemiologic investigations proposed a working hypothesis that person-to-person transmission originated from a seed case in a person who probably acquired infection through environmental exposure during travel in Argentina before boarding the ship on April 1 (10). By July 2, a total of 13 ANDV cases had been identified, including 12 laboratory-confirmed and 1 probable case; 3 of those cases were fatal (10). 

According to the initial WHO notification for the outbreak on May 2, public health and control measures, including contact tracing, case isolation, clinical care, and medical evacuation of symptomatic passengers, had been implemented onboard the ship (11). By using historical contact tracing data, we aimed to estimate key epidemiologic characteristics of person-to-person transmission of ANDV, including the serial interval (SI) distribution and transmission heterogeneity, given that those traits strongly shape outbreak size.

(SNIP) 

We identified a total of 88 case-clusters from the included studies, among which 50 (56.8%) were not associated with any secondary person-to-person transmission events. After accounting for variations across lineages or strains, the pooled estimate of Rt was 0.74 (95% credible interval [CrI] 0.28–1.29) and the estimate of k was 0.64 (95% CrI 0.36–1.16). Apart from inherent differences among ANDV lineages or strains, the substantial variation in Rt across lineages or strains could also be attributed to differences in study settings and individual-level heterogeneity in reproduction numbers (5).

We estimated that 23.4% (95% CrI 15.1%–30.3%) of the cases generated 80% of the transmission events, suggesting the person-to-person spread of ANDV exhibited relatively high heterogeneity, although it appeared lower than that observed for other pathogens known for superspreading events, including SARS-CoV, SARS-CoV-2, Middle East respiratory syndrome coronavirus, and Ebola virus (13,14).

(SNIP)

Conclusions

In summary, our results provide insights into the person-to-person transmission potential of ANDV, which exhibited substantial heterogeneity. We found a low but significant chance of observing a relatively large-scale ANDV outbreak in a rodent-free setting consisting of close contacts, which might be eradicated across a few generations of person-to-person transmission. Because no vaccine or antiviral treatment for ANDV infection is currently available, continuous surveillance of person-to-person transmission risk of ANDV is essential for preparedness against future outbreaks.

Dr. Guo is an associate professor in the School of Public Health, Tianjin Medical University, Tianjin, China. His primary research interests include epidemiology and transmission dynamics of emerging infectious diseases.

Simply put, while most ANDV outbreaks are likely to sputter out relatively quickly, there is enough variability in the transmission of the virus that occasional larger outbreaks are possible. 

For more on superspreader events you may wish to revisit:

MMWR Early Release: COVID-19 Superspreading Event In A Church Choir

CDC Update: Rapid Assessment Of COVID Outbreak At 2023 EIS Conference

Ziad Memish: Two MERS-CoV Hospital Super Spreading Studies

The Lancet: Mapping The Korean MERS-CoV Superspreading Event

Australia Reports 1st Sea Lion Death From H5N1

 

YouTube Video ABC News

#19,333

While the last posted update on South Australia's bird flu status appears to be 3 days ago, on Sept 10th, SA's environment minister Emily Bourke announced the death of an endangered Australian sea lion due to H5N1 in the press conference above.

The sea lion recovered from Seal Bay on Kangaroo island - which was being cared for after a shark attack - reportedly died from the virus.

Location Kangaroo Island - Credit Wikipedia

 

Kangaroo Island is home to a number of marine mammals which are known to be susceptible to avian flu (see Preprint: Mass mortality of southern elephant seals during multi-species outbreak of HPAI H5N1 on sub-Antarctic Heard Island), including:

• Australian sea lion.

• Australian fur seal.

• New Zealand fur seal.

• Bottlenose dolphin and common dolphin. 

While Australia's reporting on avian flu has changed; counting events rather than individual H5-positive tests, the numbers continue to rise steadily. 

So far, the virus has not been reported in poultry or other livestock, but the risks to australia's fauna remains high, and only a fraction of the nearly 42,000 hotline reports have been investigated. 

Canada: CFIA Reports 1st HPAI Poultry Outbreak SInce May

Screenshot CFIA

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While HPAI H5 no longer completely retreats each summer, the warmer months of the year usually see far less activity than the fall and winter.  And each fall, as we await the arrival of the annual southbound migration of birds, we ponder what changes that might bring (see H5Nx: Reassort & Repeat).

In the 2023-2024 avian flu season, we famously saw the emergence of a `bovine' H5N1 genotype B3.13, which has since infected (at least) 1,179 cattle herds across 20 states. 

Avian flu's return in the fall of 2024 brought with it a far more aggressive poultry/wild bird strain (D1.1) (which can also infects humans), along with a spate of oseltamivir resistant outbreaks in Canada. 

Abrupt Shift in H5N1 Genotypes in Wild Birds in US/Canada

Nature https://www.nature.com/articles/s41591-026-04300-1

Last fall - while both D1.1 and B3.13 continued to dominate - we saw the first known human infection with HPAI H5N5 in a backyard bird keeper in Washington State.  

While each fall doesn't guarantee a new wrinkle in the avian flu story, we often first notice big changes in the makeup and behavior of avian flu when migratory birds return from their high latitude roosting spots (see Sci Repts.: Southward Autumn Migration Of Waterfowl Facilitates Transmission Of HPAI H5N1).

We've already witnessed a noticeable uptick in outbreaks in commercial and backyard poultry in the United States over the past couple of weeks (see USDA dashboard below).

To this we can add Canada's first poultry outbreak since May 16th, a poultry farm in the rural municipality of De Salaberry, in Manitoba.  

Canada's first poultry outbreak of the new season comes at roughly the same time as last year (Sept 9th), and considerably earlier than the first Canadian outbreak of fall 2024 (Oct 21st).

Whether this fall brings anything substantially different remains to be seen, and unfortunately, we probably won't learn about any genetic changes for several months. As we saw last year, in Nature: Lengthy Delays in H5N1 Genome Submissions to GISAID, the average delay in submitting sequences to GISAID was 7 months (228 days), with some countries taking nearly 2 years.

  

And genetic sequences - even when they are submitted to GISAID - are often devoid of crucial metadata (i.e. collection date, exact location, host-specific information, etc.), limiting their value to the scientific community.

For now, we'll have to content ourselves with less specific data; where, when, the size, and the type of outbreak (commercial poultry, backyard flocks, livestock, peridomestic mammals, or even humans). 

In the meantime, if you raise backyard birds, or frequent live markets, now is a good time to familiarize yourselves with the risks of avian flu, and the things you can do to reduce those risks.

UF/IFAS Extension: What Backyard Flock Owners Need to Know about Bird Flu (Influenza H5N1)

Eurosurveillance: Emergence and spread of NA-I223V and NA-S247N double-mutant A(H1N1)pdm09 influenza viruses with reduced oseltamivir susceptibility in the Netherlands and beyond, 2023 to 2026

 

#19,331

Regular readers know that we've been following an uptick in reports of  `reduced susceptibility' of the seasonal H1N1 flu virus to the antiviral drug oseltamivir (aka `Tamiflu') around the globe for the past 3 years.

In March 2024 The Lancet published - Global Emergence of Neuraminidase Inhibitor-Resistant Influenza A(H1N1)pdm09 Viruses with I223V and S247N Mutations - which reported a much higher incidence of oseltamivir resistance among samples tested in Hong Kong in 2023. 

Instead of the H275Y mutation which caused nearly total resistance in 2008, these viruses carried dual I223V/S247N mutations which together produced a ≈ 10-fold reduced inhibition by oseltamivir.  

Concerning, but not enough of a hit to invalidate the clinical use of the drug. 

This was followed up 3 months later by EID Journal: Multicountry Spread of Influenza A(H1N1)pdm09 Viruses with Reduced Oseltamivir Inhibition, May 2023–February 2024 which reported a ≈ 13-fold reduced inhibition by oseltamivir

In July of 2025, Virus Research: A 15-year Study of Neuraminidase Mutations and the Increasing of S247N Mutation in Spain, we looked at a study that found a sharp increase in detections of the NA:S247N mutation beginning in 2024, but not including I223V.

Last December, in Eurosurveillance: Expansion of influenza A(H1N1)pdm09 NA:S247N Viruses with Reduced Susceptibility to Oseltamivir, Catalonia, Spain, and in Europe, July to October 2025. a Rapid Communications reported on another dramatic surge in H1N1 viruses carrying the NA:S247N mutation in Catalonia Spain, and other parts of Europe.

Abrupt rise in resistance in Catalonia, Spain - fall 2025

Some weeks (see above graphic), as many as 100% of viruses tested showed this NA:S247N mutation. 

The good news, however, was that once again, a second permissive mutation - NA:I223V - was not detected in these recent Catalonia isolates. 

As for detections in the United States (see Feb 2026 blog), over the entire 2024-2025 flu season - out of 1697 H1N1 viruses tested - only one carried the NA-I223V and NA-S247N amino acid substitutions.

And reassuringly, during the first 13 weeks of the 2025-2026 flu season (Oct - Dec) the CDC reported zero elevated resistance among the first 193 H1N1 viruses tested (see FluView Wk 53).  

But shortly after the New Year we began to seen an uptick in reduced inhibition detections in the United States. By late February (FluView week 7) - based on 517 H1N1 isolates tested since October - the CDC reported 10 isolates with reduced inhibition and 4 with highly reduced inhibition (due to NA:H275Y).

In early June we looked at the last full FluView report of the 2025-2026 flu season, which reported a total 20 reduced inhibition results, and 11 highly reduced results:

Nine A(H1N1)pdm09 viruses had NA-H275Y amino acid substitution conferring highly reduced inhibition by oseltamivir and peramivir. Nineteen A(H1N1)pdm09 viruses had amino acid substitutions NA-I223V and NA-S247N and showed reduced inhibition by oseltamivir. One A(H1N1)pdm09 virus had amino acid substitutions NA-I223T and NA-S247N and showed reduced inhibition by oseltamivir. Two A(H3N2) viruses had amino acid substitution NA-E119V conferring highly reduced inhibition by oseltamivir. Three B viruses had amino acid substitution NA-M464T and showed reduced inhibition by peramivir.

While the number of S247N+I223V mutations remains low (2.1%), this was more than a 35-fold increase over the previous year. And equally concerning - after an extended absence - the tag team of S247N+I223V was being reported again in a newer NA-clade H1N1 virus.

All of which brings us to this week's Eurosurveillance dispatch, which reports on a similar rise of S247N+I223V in the Netherlands; first in 2024 and then - after a brief absence - again in 2026.

Due to its technical nature, I've only posted some excerpts. Those seeking a deeper dive will want to follow the link to read it in its entirety.   I'll have a postscript after the break.

Emergence and spread of NA-I223V and NA-S247N double-mutant A(H1N1)pdm09 influenza viruses with reduced oseltamivir susceptibility in the Netherlands and beyond, 2023 to 2026 

Zandra Felix Garza1 , Dirk Eggink1 , Mariam Bagheri1 , Sharon van den Brink1 , Gabriel Goderski1 , Mark Pronk2 , Pascal Lexmond2 , Mariëtte Hooiveld3 , Rianne van Gageldonk-Lafeber1 , Björn Koel2 , Ron Fouchier2 , Adam Meijer1

In 2023/24, a neuraminidase (NA)-clade of A(H1N1)pdm09 influenza viruses carrying the NA-I223V amino-acid substitution emerged, followed by acquisition of NA-S247N [1-3]. Both substitutions individually increase the 50 per cent inhibitory concentration (IC50) by oseltamivir but the resulting IC50-fold-increase remains below the threshold for reduced inhibition (RI) (IC50-fold-change > 10 compared with median IC50 of wildtype (WT) viruses [4]). In double-mutant viruses, the substitutions act synergistically, causing phenotypically RI by oseltamivir, but not by zanamivir [1,2].

In late 2025, Saubi et al. [5] reported re-emergence of A(H1N1)pdm09 viruses carrying NA-S247N in Spain and elsewhere in Europe. Here, we show the re-emergence of A(H1N1)pdm09 NA-I223V and NA-S247N double-mutant viruses in 2025/26 in the Netherlands and assess their phenotypic susceptibility, global spread and evolution from 2023 to 2026.

Discussion

The recent expansion of A(H1N1)pdm09 influenza virus clusters carrying either NA-I223V (2023/24) or NA-S247N (2025/26) was followed in both seasons by the emergence and spread of double-mutant viruses combining these substitutions, causing RI by oseltamivir. This pattern suggests a fitness advantage of single and double mutants [2], although they have not become permanently dominant. The appearance of double mutants is likely independent of antiviral selection, as NA inhibitors are only sporadically used in several countries reporting high proportions of these viruses and such viruses have not been reported from Japan, where NA inhibitor use by capita is highest [14,15], in publicly available GISAID data.

NA-I223V and NA-S247N, alone or in combination, have been proposed as changes that compensate for the fitness cost of NA-H275Y, which confers highly RI by oseltamivir [16]. Both substitutions individually, and especially together, further drastically reduce inhibition by oseltamivir in NA-H275Y mutants [16,17].

During the study period, NA-S247N together with NA-H275Y was detected 33 times and once as a triple mutant including NA-I223V, confirming that such variants showing very high RI can arise and are of concern. Phenotypic data for Dutch viruses show that the 2025/26 NA-I223V combined with NA-S247N double mutant display oseltamivir RI while retaining normal inhibition by zanamivir, similar to the 2023/24 double-mutant and reports elsewhere [1,2,17]. The shown impact of different reference IC50 values on fold-change calculations highlights the need for caution in using WT data and interpreting IC50 values near the 10-fold RI threshold, given the arbitrary nature of the defined threshold values [11]. Synergistic IC50 increases in double mutants should nonetheless be carefully monitored and reported. The impact of these double mutants on clinical management of influenza patients is unknown and should be part of future studies.

Dominance of double mutants within defined HA/NA-subclusters, with gradual accumulation of additional changes, suggests global dissemination from one or several initial emergence(s) or introduction(s), although occasional detection of double mutants in other NA-clades indicates that parallel evolution of similar A(H1N1)pdm09 variants showing oseltamivir RI is also possible. Awareness is therefore warranted whenever NA-I223V or NA-S247N become fixed in spreading subclusters. The recent emergence and spread of NA-S247N in NA-clade D.1 on an HA-clade D.3.1.1 background should be closely monitored during the progressing 2026 southern hemisphere and coming 2026/27 northern hemisphere seasons. Similar to the abundancy of NA-clade D.3 with NA-S247N in HA-clade D.3.1.1 background, HA-clade D.3.1.1 viruses could provide a favourable context for the expansion of such viruses carrying NA of clade D.1 with NA-S247N.

Our global assessment is limited by reliance on non‑embargoed sequences and metadata in GISAID. Country and regional representativeness depends on local laboratory capacity to sequence at least the HA and NA gene segments, and on whether data are submitted to GISAID or other databases (e.g. GenBank, Pathoplexus). While WHO Collaborating Centres partly compensate for gaps at NICs by sequencing of representative viruses shared by NICs and submitting these sequence data to GISAID, our analysis may still over‑estimate mutant presence in some regions and under‑estimate it in others. Our study outcomes should therefore be interpreted in light of these sampling and database‑related limitations.

Conclusion

Our findings highlight the need for continued surveillance on the evolution of A(H1N1)pdm09 influenza viruses and the possible emergence of mutants, especially double and triple ones, with antiviral (highly) RI. The capacity to phenotypically evaluate the impact of individual and combinations of amino-acid substitutions associated with antiviral (highly) RI remains a critical component of this surveillance.

        (Continue . . . )

In 2024 we saw sporadic reports of I223V+S247N in H1N1 NA-Clade C.5.3.3 viruses which produced a 12-13 fold reduction in oseltamivir susceptibility. By 2025 they had largely disappeared, replaced by reports of less impactful single S247N mutations spreading in Europe.

Fast forward to 2026 and we find that the I223V+S247N combo has reappeared in a genetically different NA-clade (D.3) H1N1 virus, suggesting the earlier appearance was more than just a fluke. 

Where this story goes from here is anyone's guess, but should the I223V+S247N combo team up with additional permissive mutations (including H275Y) - and also become more prevalent in seasonal H1N1 - it could compromise the clinical effectiveness of our primary influenza antiviral drug; oseltamivir.   

A lot of `ifs', but given the stakes, this is a story very much worth following. 

The CDC should resume reporting on antiviral mutations in October, and hopefully we'll be getting similar reports out of Europe later this fall.  

South Korean CDC Issues Early Seasonal Flu Epidemic Advisory

Proportion of Suspected Influenza Cases in Clinics
( As of Sep 5, 2026 ; Persons / 1,000 Persons )

#19,330

Typically, nations in the Northern Hemisphere don't even begin tracking seasonal  influenza seriously until October 1st; the assumed start of each year's flu season.  Our own CDC only publishes an abbreviated  FluView report during the summer months (see Week 20 2026 notice below).

Two weeks ago (Aug 28th), however, Japan announced the earliest start since the 2009 H1N1 pandemic for their flu season (see Japan MHLW Reports Unusually Early Start to the Fall Flu Season), while Taiwan reported this week `. . . emergency room visits reached 11.2%, exceeding the epidemic threshold (11.0%), indicating the start of the epidemic period.'

Hong Kong - which often reports a biphasic flu season - continues to report a strong summer wave of influenza, and China reports elevated flu activity in their southern provinces for week 36. 

This unusual wave of early flu continues, as today South Korea's CDC issued an early seasonal flu advisory, citing a 4x higher rate of ILI (Influenza-like Illness)  consultations this week than a year ago. 

        (translation)

Influenza Epidemic Advisory Issued for 2026-2027 Season; Early Outbreak Compared to Previous Years, Response Strengthened for Students and High-Risk Groups (Fri, Sept. 11)

Date written 2026.09.11
Last modified date 2026.09.11
Department in charge Infectious Disease Control Division
contact 043-719-7141

Influenza Epidemic Advisory Issued for 2026-2027 Season; Early-than-usual Outbreak, Response Strengthened for Students and High-Risk Groups

- With the start of the season, “2026-2027 Season Influenza Epidemic Advisory Issued” starting September 11 (Fri)

- Although COVID-19 levels are lower than the same period last year, the number of hospitalized patients continues to increase

- Conducted a review of the epidemic status and response measures together with experts and relevant ministries

Emphasize wearing a mask when experiencing respiratory symptoms and urge adherence to preventive measures against respiratory infections, such as covering the mouth and nose with a tissue or sleeve when coughing; high-risk groups need to visit a medical institution early for appropriate treatment if they experience fever or respiratory symptoms.

The Korea Disease Control and Prevention Agency (Director Lim Seung-kwan) announced that, as the incidence of influenza is higher than in previous years, it held the "9th Meeting of the Inter-Ministerial Joint Task Force on Respiratory Infectious Diseases" with medical experts and relevant ministries (Ministry of Health and Welfare, Ministry of Food and Drug Safety, Ministry of Education) to review the current status of influenza and COVID-19 outbreaks and response measures, and issued an "Influenza Epidemic Advisory" starting at 00:00 on September 11 (Fri).

(Criteria for issuing an epidemic advisory for the '26-'27 season) Issued following expert consultation when the proportion of suspected influenza (ILI) cases exceeds the epidemic threshold for the relevant season and the influenza virus detection rate is 5% or higher.

※ Influenza-like illness (ILI): Cases where a cough or sore throat is present along with a fever of 38°C or higher

【 Current Status of Influenza and COVID-19 Outbreaks 】

According to the results of the sample surveillance of influenza-like illness (ILI) at clinics, the proportion of influenza-like illness cases in the 36th week of 2026 (Aug. 30–Sept. 5) was 25.3 per 1,000 outpatients, exceeding the epidemic threshold for this season (12.9) and rapidly increasing to a high level compared to the same period last year (6.6).

* (ILI rate over the last 4 weeks) Week 33 7.5 → Week 34 9.2 → Week 35 13.3 → Week 36 25.3

※ The influenza surveillance system operates from week 36 to week 35 of the following year (September to August of the following year) as a single season.

Incidence is increasing across all age groups, with a relatively high and rapid increase observed in the school-age and infant/child age groups, in the order of 7-12 years (75.1 people), 1-6 years (49.8 people), and 13-18 years (31.3 people).

* 7-12 years (75.1 people) > 1-6 years (49.8 people) > 13-18 years (31.3 people) > 0 years (24.0 people) > 19-49 years (23.5 people) > 50-64 years (11.8 people) > 65 years and older (8.8 people)

The number of inpatients at sample medical institutions at the hospital level in week 36 was 300, which is about double the number from last week (166) and shows a higher incidence compared to the same period last year (23 in week 36 of '25), and the age group of inpatients aged 65 or older accounts for the largest proportion at 60.0%.

* (Number of hospitalized patients in the last 4 weeks) Week 33: 78 → Week 34: 89 → Week 35: 166 → Week 36: 300

The detection rate of influenza viruses is also showing an increasing trend*, and the influenza virus currently in circulation is Type A (H1N1) pdm09, which is similar to the vaccine strain for this season** and has been confirmed to have no mutations affecting resistance to treatment.

* (Detection rate over the last 4 weeks) Week 33 5.4% → Week 34 10.0% → Week 35 12.3% → Week 36 16.3%
**The virus used to produce the influenza vaccine recommended by the World Health Organization (WHO)

(SNIP)

The Korea Disease Control and Prevention Agency plans to sequentially implement the national influenza vaccination program starting Monday, September 21, but it also plans to review measures to adjust the vaccination schedule, focusing on high-risk groups including immunocompromised individuals, by comprehensively considering the epidemic situation and vaccine supply schedule.

(Continue . . . )

Many countries won't begin to ramp up their fall flu vaccination campaigns until October (see UKHSA blog), and as cited above, South Korea's target date is still 10 days away. 

 

Given that this year's fall flu vaccines have been updated to reflect recent antigenic changes observed in all 3 seasonal flu types (see WHO Recommendations for Influenza Vaccine Composition), community immunity against this fall's array of circulating flu viruses may be low.  

Complicating matters, South Korea is also reporting low, but rising, rates of COVID infection:

In addition, the number of COVID-19 inpatients at hospital-level sample surveillance medical institutions in the 36th week of 2026 (Aug. 30–September 5) was 193, which is lower than the same period of the previous year (433 in the 36th week of 2025), but has been continuously increasing since August, and by age group, the elderly aged 65 or older accounted for the largest proportion at 65.3% of the total.

* (Number of hospitalized patients in the last 4 weeks) Week 33: 57 → Week 34: 61 → Week 35: 115 → Week 36: 193

COVID wastewater surveillance (see chart below) shows increasing detection in sewage.

While none of this tells us much about the severity of this year's flu season, it does suggest that it may be upon us sooner than we expect.  Of course, what happens in Asia isn't necessarily a harbinger for what we see in North America or Europe, but it is definitely worthy of our attention. 

The U.S. CDC should publish their updated Respiratory Virus Activity Levels report later today, but last week's report showed very little flu, and low, but rising COVID activity. 

 

Stay tuned. While things are quiet now, it could be a bumpy fall. 

The Lancet Regional Health Europe (Comment): If the EU is serious about One Health, it must ban fur farming

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Last month, in That Touch of Mink Flu (H5N1 in Utah Edition), we looked at the latest report of an avian flu virus detected in 7 captive (presumably farmed, but details are scant) mink here in the United States.  

This time, the viral culprit was avian H5N1, but over the years we've followed numerous reports of zoonotic pathogens detected on fur farms, with some even spilling over into humans.  

While mink are most frequently cited, fox, raccoon dogs, and rabbits are also farmed.  Some early reports include:

• As far back as 1984, a large outbreak in Swedish mink farms was found to be due to the H10N4 avian virus.

• In 2006 CIDRAP reported on a European mink found infected with an aggressive form of the H5 flu virus in the Blekinge region of southern Sweden near where H5N1 had been detected in wild birds.
• In 2007, an antigenically distinct H3N2 Swine Influenza was detected in Canadian Mink, reported in a 2009 Journal of Clinical Microbiology study called Characterization of a Canadian Mink H3N2 Influenza A Virus Isolate Genetically Related to Triple Reassortant Swine Influenza Virus.

• In 2009's That Touch Of Mink Flu, at least 11 mink farms in the Holstebro municipality of Denmark were reported to be infected with a variant of the human H3N2 virus.
• 2017's That Touch Of Mink Flu (H9N2) - Revisited looked at the spread of LPAI H9N2 in mink.

It was in 2020, however, when a unique mink-variant of SARS-CoV-2 was discovered spreading through millions of farmed mink in Denmark - which then jumped to humans - that the alarm bells were really raised (see EID Journal: SARS-CoV-2 Transmission between Mink (Neovison vison) and Humans, Denmark).

This prompted authorities to order the depopulation of 17 million mink (see Denmark Orders Culling Of All Mink Following Discovery Of Mutated Coronavirus), to temporarily lock down North Jutland (where most of the human cases had been identified) and led to some countries banning travel to and from Denmark.

 

Denmark wasn't alone, as fur farms in Spain, the United States, Canada, and several other European countries all eventually reported outbreaks of COVID, with some evidence of spillovers into humans (see CDC: Investigating Possible Mink-To-Human Transmission Of SARS-CoV-2 In The United States).

Alarms were raised again in the fall of 2022 when H5N1 began spreading rapidly through a large mink farm in Spain (see Eurosurveillance: HPAI A(H5N1) Virus Infection in Farmed Minks, Spain, October 2022).

This mink-derived H5N1 virus from Spain carried a rare mutation (PB2-T271A), which is believed to `enhance the polymerase activity of influenza A viruses in mammalian host cells and mice'. In 2023 the CDC issued an IRAT Risk Assessment On Mink Variant of Avian H5N1, finding its scores had risen in 6 of the 10 parameters used to evaluate their zoonotic potential.

The following year (2023) Finland's fur industry was hit unusually hard by HPAI H5N1, with more than 70 fur farms infected, and > 500,000 animals culled, prompting  Finland's Institute for Health and Welfare (THL) to warn `Avian influenza poses a risk to public health – improvements to health security needed at fur farms'.

During the height of this outbreak, we looked at an excellent opinion piece (see PNAS: Mink Farming Poses Risks for Future Viral Pandemics) penned by two well known virologists from the UK (Professor Wendy Barclay & Tom Peacock) on why fur farms - and mink farms in particular - are high risk venues for flu.

Since then we've seen several other notable outbreaks, including SFTS in Chinese Farmed Mink and a reassorted swine and human-origin H3N2 in Canadian farmed mink.  Many farms, and governments, are reluctant to provide details on outbreaks, and so we are likely only seeing the tip of the iceberg. 

While some EU countries have taken steps to phase out or ban fur farming, the industry continues in many parts of the world, including China, Russia, the United States, Canada and parts of the EU.

All of which brings us to a commentary, published two weeks ago in The Lancet Regional Health: Europe, which calls upon the EU to ban fur farming due to the public health risks they pose. 

If the EU is serious about One Health, it must ban fur farming
Joanna Swabea Send email to jswabe@humaneworld.org ∙ Chris Walzerb,c ∙ Benjamin Roched,e ∙ Arnaud Fontanetf ∙ Thijs Kuikeng ∙ Manon Lounnasd ∙ et al. 
Received August 4, 2026; Accepted August 20, 2026; Published August 29, 2026
DOI: 10.1016/j.lanepe.2026.101848 External Link 
Copyright: © 2026 The Author(s). Published by Elsevier Ltd.
User License: Creative Commons Attribution – NonCommercial – NoDerivs (CC BY-NC-ND 4.0) | Elsevier's open access license policy

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The One Health approach, which recognises the fundamental interconnectedness of human wellbeing with that of other animals and the environment, is a keystone of the European Union’s health policy.1 While the prevention of zoonotic diseases, including pandemics, is a core objective of this policy, the European Commission paradoxically seems reluctant to take decisive action to address one of the highest risk sources within its borders precisely at the moment when it finally can do so. 

Specifically, the Commission is currently considering legislation to ban fur farming in the EU, prompted by a 2023 European Citizens’ Initiative on the issue that had the support of more than 1.5 million EU citizens.2 A decision was due by March 2026, but the Commission has thus far delayed issuing one. There are indications that it may instead propose minimum welfare standards for the intensive production of fur-producing animals.2 However, doing so would be a grave mistake for animals and humans alike.

Fur farming is a niche industry producing non-essential luxury products, yet it poses a threat to human health. It is an avoidable anthropogenic system that concentrates large numbers of genetically homogeneous, susceptible wild fur-bearing animals in close confinement creating the conditions that favour the introduction, amplification, adaptation and spillover of pathogens to humans (spillover being the transmission of a pathogen from one vertebrate species to another).3 Once a pathogen is introduced to captive animals on these farms (whether from humans, contaminated feed, or from wildlife attracted to the farms), it can spread easily and eventually infect humans working on these farms.3

Fur farms have already been implicated in serious outbreaks in multiple countries across Europe. In 2020, for example, mink became infected with SARS-CoV-2 on multiple mink farms in the Netherlands, with subsequent “spillback” of SARS-CoV-2 from mink into humans.4 SARS-CoV-2 outbreaks were also identified on 290 mink farms in Denmark, resulting in hundreds of COVID-19 cases in humans caused by mink variant strains.5 The Danish government responded by culling the country’s entire farmed mink population — 17 million animals — while compensating mink farmers over €3 billion for their losses.6,7 It also suspended mink farming activities, but these have since resumed.

Lessons learned?

The lesson learned from COVID-19 was not that more surveillance could make fur farms safe, but rather that surveillance documented the predictable consequences of a production system that facilitates pathogen introduction, amplification and adaptation. This cyclical reactive response followed by a return to business as usual reflects a pervasive global health security framework that is unsustainable. One Health is fundamentally about investing upstream, reducing the conditions that give rise to disease emergence rather than continually paying for downstream surveillance and response, after damage is already done. Continuing to invest public resources in managing risks generated by an economically failing niche industry is difficult to reconcile with the EU’s preventive One Health ambitions.7

Outbreaks of highly pathogenic avian influenza A(H5N1) have also affected fur farms. In 2023, infections were confirmed on multiple fur farms in Finland, likely introduced to captive animals from wild birds.8 Spain also recorded an H5N1 outbreak on a mink farm in 2022, with possible viral mutation on the farm.9 An especially concerning aspect of influenza in mink is that they are susceptible to influenza viruses originating from both birds and humans. They can therefore serve as a host in which genetic reassortment occurs, which is a known route for the evolution of influenza viruses that can cause pandemics.3

These outbreaks have accelerated the decline of the EU fur farming industry. By 2024, fur production had dropped to an annual low of 6.3 million pelts, corresponding to €183 million in sales — a decline of 92% compared with the previous decade.7 Meanwhile, the industry costs European society approximately €446 million per year after accounting for its environmental and public health consequences.7 Consumers and fashion brands are also turning away from fur, and 24 (out of 27) EU Member States have already enacted production bans or restrictions on fur farming.7

The public moral concerns about the welfare of animals on fur farms, which precipitated these restrictions, are also well-founded. Indeed, the European Food Safety Authority concluded through an independent scientific investigation that, in the current caged fur farming system, the most serious adverse welfare consequences for mink, foxes, raccoon dogs and chinchillas cannot be prevented or substantially mitigated in the majority of cases.10 It is highly doubtful that changing cage dimensions, introducing enrichment requirements or inspection regimes will achieve meaningful animal welfare improvements. What it certainly will not do is remove the core epidemiological hazards posed by fur farming, namely keeping large numbers of captive bred-wild mammals in intensive systems where viruses can circulate and evolve.

If the European Commission intends to do more than merely pay lip service to One Health, it must accept accountability and take action before the next zoonotic crisis occurs. Banning fur farming would demonstrate what effective One Health policy looks like in practice: eliminating an avoidable anthropogenic source of zoonotic disease risk, while responding to citizens' concerns, thereby establishing Europe as a global leader in upstream pandemic prevention.

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The concern, particularly with high density animal farms, is that it provides the virus with an ideal environment to spread from mammal to mammal. Long chains of infection (see graphic below) can provide the virus with additional opportunities to adapt to a new host species, furthering its evolution.

 Admittedly, the next pandemic could arise from any farmed livestock (poultry, swine, cattle, etc.), or even from the wild. We can never truly pandemic-proof our world. 

But fur farming practices are arguably more conducive to the generation and spread of zoonotic viruses, as mink are highly susceptible to influenza and coronaviruses, and it is common in many countries to feed raw poultry or poultry meat products to mink raised in captivity.

Whether we can summon the political will to do something about this threat remains to be seen.