#18,279
Overnight the WHO is reporting on a swine variant (H1N1v) case out of Vietnam - that country's first detection - in a 70-year-old female from Son La province. She reportedly had underlying medical conditions, but had few contacts with other people, and no known exposure to pigs.
She was hospitalized on June 1st, diagnosed with pneumonia, and tested positive for influenza A on the 5th (no subtype determined). She died 6 days later.
Subsequent genetic sequencing of the sample in early August revealed she had been infected with a swine variant H1N1 virus. Their (delayed) epidemiological investigation has yet to determine her exposure, or to find any of her limited contacts with symptoms.
While most swine variant infections can be linked to contact with pigs, we occasionally see isolated cases where no such connection can be established. Three years ago, we saw a similar case in Europe (see EID Journal: Reassortant Influenza A(H1N1)pdm09 Virus in Elderly Woman, Denmark, January 2021) of a woman in lockdown during COVID, who was infected from an unknown source.
While swine variant infections are only infrequently reported, swine variant influenza infections are indistinguishable from seasonal flu without highly specialized testing, which few countries tend to do.Even here in the United States it is assumed we only detect a small percentage of cases (see CID Journal: Estimates Of Human Infection From H3N2v (Jul 2011-Apr 2012)). So far in the 2023-2024 flu season, only 7 swine variant infections (four A(H1N2)v, two A(H3N2)v, and one A(H1N1)v) have been reported in the United States.
First the link and some excerpts from the WHO report, after which I'll return with a postscript.
Influenza A(H1N1) variant virus - Viet Nam
4 September 2024
Situation at a glance
On 19 August 2024, the Viet Nam National Focal Point (NFP) for International Health Regulations (IHR) notified the World Health Organization (WHO) of a laboratory-confirmed human case of infection with swine-origin influenza A(H1N1) variant (v) virus, in the province of Son La, a northern mountainous province in Viet Nam bordering the Lao People's Democratic Republic. This is the first-ever reported human infection caused by influenza A(H1N1)v virus in Viet Nam. The source of exposure to the virus is currently unknown. According to the International Health Regulations (IHR) 2005, a human infection caused by a novel influenza A virus subtype is an event that has the potential for high public health impact and must be notified to WHO. Based on the currently available information, WHO assesses the current risk to the general population posed by this virus as low. WHO continues to stress the importance of global surveillance to detect virological, epidemiological and clinical changes associated with circulating influenza viruses that may affect human (or animal) health, and timely virus sharing for risk assessment.
Description of the situation
On 19 August 2024, the Viet Nam IHR NFP notified WHO of a laboratory-confirmed human infection with a swine-origin influenza A(H1N1)v virus. The patient was a 70-year-old female with underlying medical conditions, from Son La province, a northern mountainous province in Viet Nam bordering the Lao People’s Democratic Republic.
The patient developed fever, fatigue, and loss of appetite one week after returning from spending a month in her home village in Hung Yen province. On 1 June 2024, she was admitted to a district hospital due to persistent symptoms and was diagnosed with pneumonia in addition to her underlying medical conditions. On 5 June, a rapid test confirmed influenza A. On the same day she was transferred to the National Hospital for Tropical Diseases (NHTD) where she underwent treatment for six days but died on 11 June.
A sample collected on 5 June was tested through reverse transcription-polymerase chain reaction (RT-PCR) which confirmed influenza A virus on 18 June, but subtyping was not determined. On 1 August, genomic sequencing identified influenza A(H1N1)v virus, which was confirmed by the WHO Collaborating Centre (WHO CC) for influenza at the United States Centers for Disease Control and Prevention (US CDC) on 5 August. Further characterization of the virus is ongoing.
Epidemiological investigations revealed that the patient lived alone and had limited contact with a few villagers and caregivers during her illness in Son La province. From June to 11 August, there have been no reports of respiratory symptoms among contacts, including healthcare workers of the case, or outbreaks in the community in Son La where the patient lived. There have been no disease outbreaks among livestock, including pigs, around the case’s residence in Son La. There have been no official or unofficial reports from the case’s home village in Hung Yen province. At the time of reporting, the source of exposure to the virus remains unknown.(SNIP)
WHO risk assessment
Human infections with swine-origin influenza viruses have been reported in recent years from many countries. Most human cases with influenza A(H1N1)v virus infection result from exposure to swine influenza viruses through direct contact with infected swine or indirectly through contaminated environments. However, a few cases have been reported without an apparent source of exposure to swine in the weeks prior to illness onset. Because these viruses continue to be detected in swine populations worldwide, further human cases following direct or indirect contact with infected swine can be expected.
Limited, non-sustained human-to-human transmission of variant influenza viruses has been described, although ongoing community transmission has never been identified. Current evidence suggests that these viruses have not acquired the capacity for sustained transmission among humans. According to the information available thus far, no further human cases of infection with A(H1N1)v viruses associated with this case have been detected.
Based on the available information, WHO assesses the current risk to the general population posed by this virus to be low. Further virus characterization is ongoing. The risk assessment will be reviewed should further epidemiological or virological information become available.
While this is the first confirmed human infection with a swine variant virus in Vietnam, last summer (2023) we looked at a study (see EID Journal: Long-term Epidemiology and Evolution of Swine Influenza Viruses, Vietnam), which reported on swine influenza surveillance conducted at a slaughterhouse in Hanoi, Vietnam, which received pigs from roughly 2 dozen provinces.
This surveillance (conducted between 2013 and 2019) found repeated introductions of both human and swine influenza viruses into the herds, and documented the detection of a new H1-δ1a strain which may have increased zoonotic potential.
Globally, surveillance ranges from suboptimal to nonexistent, making it difficult to quantify the threat.
As the following chart illustrates, half of the world's pigs are grown in China, where the CDC's #1 threat on their IRAT list (Swine-Variant EA H1N1 `G4' virus) circulates (with many others).
The good news is that currently circulating swine variant viruses haven't become biologically `fit' enough spark a pandemic. In order to be successful, they need to be able to replicate and transmit on par with already circulating human flu viruses.
The bad news is - as we saw in 2009 with the H1N1 pandemic - the first sign we may see that a swine-variant virus has evolved into a pandemic threat may not come until days or even weeks after the virus has begun its world tour.
