Chinese researchers have now discovered a new variety of swine flu with "pandemic potential". The researchers reported on influenza virus surveillance in pigs from 2011 to 2018 and came across a genotype G4 that "resembles the 2009 H1NI pandemic".
According to the study published in the journal PNAS: "Pigs are considered as important hosts or mixing vessels for the generation of pandemic influenza viruses. Systematic surveillance of influenza viruses in pigs is essential for early warning and preparedness for the next potential pandemic."
The report goes on to say that the researchers identified a "reassortant EA H1N1 virus possessing pdm/09 and TR-derived internal genes, termed as G4 genotype", which has become predominant in swine populations since 2016. "Similar to pdm/09 virus, G4 viruses have all the essential hallmarks of a candidate pandemic virus."
According to the scientists, including those from the Chinese Center for Disease Control and Prevention, these G4 viruses bind to receptor molecules in human cells, and can replicate in the outer layer of the respiratory system. They demonstrated that the newly identified virus can efficiently infect ferrets via aerosol transmission, causing severe clinical symptoms in them like sneezing, wheezing, coughing, and a mean maximum weight loss ranging from 7.3 to 9.8 per cent of the mammals' body mass.
G4 was found to be highly infectious, with capabilities of transmission to humans. The report noted as a cause of concern that serological surveys showed that 10.4 per cent (35/338) of swine workers tested positive for the G4 EA H1N1 virus. "Participants 18 to 35 years old had 20.5 per cent (9/44) seropositive rates, indicating that the predominant G4 EA H1N1 virus has acquired increased human infectivity. Such infectivity greatly enhances the opportunity for virus adaptation in humans and raises concerns for the possible generation of pandemic viruses."
Pre-exisiting immunity might not matter much, according to the report. "Similar to pdm/09 virus, G4 viruses bind to human-type receptors, produce much higher progeny virus in human airway epithelial cells, and show efficient infectivity and aerosol transmission in ferrets. Moreover, low antigenic cross-reactivity of human influenza vaccine strains with G4 reassortant EA H1N1 virus indicates that preexisting population immunity does not provide protection against G4 viruses."