The HA1 Subunit of Haemagglutinin Protein (HA) from the Influenza A – G4 (EA) H1N1 virus plays a major role in the infection of a cell and is therefore a very important target for the development of antibody tests or for vaccine development. The HA1 domain binds to the cell surface receptor and thus brings virus particle into it. The HA1 protein belongs to the Class I viral fusion proteins and plays an important role in the determination of host range restriction and virulence. The protein is responsible for the penetration of the virus into the cell cytoplasm by mediating the fusion of the membrane of the endocytosed virus particle with the endosomal membrane.
Recently, a prevalent Eurasian avian-like H1N1 swine influenza virus with a potential pandemic concern was described in the journal Proceedings of the National Academy of Science (PNAS). The described genotype 4 (G4) reassortant Eurasian avian-like (EA) H1N1 virus was found in Chinese pigs and has become predominant since 2016. According to the report (Sun et. al., 2020, PNAS), similar to the pandemic 2009 H1N1 virus, G4 viruses bind to human-type receptors and therefore have the correct characteristics to cause human infections. The G4 EA H1N1 viruses have the ability to grow well in human lung cells and show efficient infectivity and aerosol transmission in ferrets. In their study (Sun et. al., 2020, PNAS), the researchers were able to show that approximately 10% of swine workers (n=338) and 4% of 230 people from the general population in China were seropositive for the G4 EA H1N1 virus. This indicated that the virus has acquired increased human infectivity and therefore greatly enhanced the possibility of virus adaptation in humans. Experts believe, that pre-existing population immunity does not provide protection against G4 viruses. Moreover, according to scientists, the G4 viruses are diverse enough that seasonal flu vaccines would unlikely provide protection or prevent a human-to-human transmission.
Until now, there have been no reports of G4 viruses spreading from human to human – a characteristic that is required for classification as a pandemic. Nevertheless, controlling the prevalent G4 EA H1N1 virus in pigs and monitoring the swine worker populations are very important. Indeed, systematic surveillance of influenza viruses in pigs is a key measure for early warning and preparing for the next potential pandemic, as was demonstrated by the emergence of the 2009 pandemic. Therefore, it is very important to be prepared and to develop antibody tests or vaccines, for detecting a potential G4 EA H1N1 virus outbreak in humans and to have the right medicine ready.