New H1N1 Swine Flu Strain Could Have Pandemic Potential

A study from China has reported that a new strain of the H1N1 swine flu virus is infecting pigs and pig farmers in the country. The virus appears to have originated in the animals and may have now spread to humans. Pigs are commonly known to be intermediate hosts for this family of influenza viruses.

The new strain, called G4 EA H1N1, is described in a study, published on June 29 in the Proceedings of the National Academy of Sciences. G4 EA H1N1 has been commonly found on pig farms in China since 2016, however, this is the first time that transmission of the virus to humans has been reported.

H1N1 is highly transmissible and caused a global pandemic in 2009 that killed 285,000 people before mutating to become a milder seasonal flu strain.

While the new H1N1 strain has reportedly infected some people without causing disease, health experts fear that this could rapidly change without warning. According to the study’s findings, the virus efficiently replicates in human airways, raising concerns that it could potentially have severe respiratory effects.

“G4 viruses have all the essential hallmarks of a candidate pandemic virus,” the study stated. The authors add that controlling the spread in pigs and closely monitoring human populations “should be urgently implemented.”

This is particularly important given that China has the largest pig population in the world, with 500 million pigs across farms in the country.

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Serological surveillance of occupational exposure among pig farmers revealed that 10.4 percent of swine workers tested positive for the G4 EA H1N1 virus. The highest rate of infection was seen in workers between the ages of 18 and 35, who had a seropositive rate of 20.5 percent.

The findings demonstrate that the G4 EA H1N1 virus acquired increased human infectivity. According to the study, “such infectivity greatly enhances the opportunity for virus adaptation in humans and raises concerns for the possible generation of pandemic viruses.”

New G4 Virus

The G4 EA H1N1 strain is a genotype 4 (G4) virus that contains a unique combination of three different viral lineages: one related to strains found in European and Asian birds (Eurasian Avian-like, or EA), the H1N1 strain that caused the 2009 pandemic (pdm/09) and a North American H1N1 that has a triple-reassortant of genes from avian, human and pig influenza viruses. ‘Reassortant’ refers to the swapping of genes between different strains of viruses that infect a single host.

The research project, led by Liu Jinhua from the China Agricultural University (CAU), involved the surveillance of pigs from 2011 to 2018, with the goal of identifying influenza strains that may have ‘pandemic potential.’

The research team analyzed close to 30,000 nasal swabs taken from pigs at slaughterhouses in ten provinces across China. They also looked at an additional 1,000 swabs from pigs at the university’s veterinary teaching hospital that exhibited respiratory symptoms.

The collected samples contained 179 different swine influenza viruses, with G4, or one of five other G strains from the Eurasian Avian-like lineage, identified as the main viral strain in the pigs. According to the paper, “G4 virus has shown a sharp increase since 2016, and is the predominant genotype in circulation in pigs detected across [the] ten provinces.”

Sun Honglei, first author on the paper, said G4’s inclusion of genes from the 2009 H1N1 pandemic “may promote the virus adaptation” that leads to human-to-human transmission. He said it is therefore, “necessary to strengthen the surveillance” of pigs in China for influenza viruses.

Infectivity and Immunity

Similar to the pdm/09 virus, G4 viruses bind to human-type receptors, produce significantly high viral loads in epithelial cells lining the human airway and show efficient infectivity and aerosol-based transmission in ferrets.

The G4 variant is particularly concerning because the majority of it is comprised of an avian influenza virus (with small bits of mammalian strains) that humans do not have any immunity against. Additionally, the researchers found that there is low antigenic cross-reactivity of current human influenza vaccine strains with the G4 EA H1N1 virus, indicating that current population immunities cannot protect against G4 viruses.

However, Martha Nelson, an evolutionary biologist at the US National Institutes of Health’s Fogarty International Center told Science Magazine that, “the likelihood that this particular variant is going to cause a pandemic is low.” Nevertheless, she added that the pandemic H1N1 strain was a definite surprise and remained unknown until the first human cases surfaced in 2009. “Influenza can surprise us,” said Nelson. “And there’s a risk that we neglect influenza and other threats at this time [of COVID-19].”

Having to deal with another pandemic on top of a current pandemic would certainly be an unprecedented challenge, but not one without any foresight, or hindsight. The Chinese researchers say they became aware of the new H1N1 swine flu being transmitted to humans back in December 2019, which is around the same time that health officials around the world were alerted of the emergence of COVID-19 in Wuhan.

Close monitoring of the new circulating G4 EA H1N1 virus will be imperative in the weeks and months to come in efforts to curb the onset of another pandemic.