Construction and comparison of different source neuraminidase candidate vaccine strains for human infection with Eurasian avian-like influenza H1N1 virus

Homologous PB1 gene promotes the replication efficiency of avian influenza H7N4 candidate vaccine virus

Background

The first and only case of human infection with the avian influenza A (H7N4) virus in China emerged in 2018. The H7N4 virus was distinct from previous H7N9 viruses and raised public concerns. Therefore, developing a suitable H7N4 candidate vaccine virus (CVV) remains crucial for potential pandemic preparedness.

Methods

We constructed a reassortant virus with a (6 + 2) genome composition, then introduced the polymerase basic protein 1 (PB1) from a wild‐type virus to develop a (5 + 3) reassortant virus through reverse genetics. We performed whole‐genome sequencing to confirm the genome stability, assessed the growth ability in MDCK cells, and analyzed virus antigenicity using hemagglutination inhibition assays. Subsequently, the effect of homologous PB1 on polymerase activity, viral protein yield, and pathogenicity was assessed.

Results

The (5 + 3) virus harbouring the homologous PB1 gene exhibited significantly improved growth characteristics, higher viral protein yield, and polymerase activity than the (6 + 2) virus. After successive passage in embryonated eggs, glutamic acid (E) substituted glycine(G) at position 218 (H3 numbering) in the hemagglutinin (HA) gene of both (5 + 3) and (6 + 2) viruses. The substitution improved the growth of the (6 + 2) virus but exhibited no significant effect or alteration on the antigenicity of the (5 + 3) virus. Moreover, the (5 + 3) virus exhibited low pathogenicity in chickens and ferrets.

Conclusion

Homologous PB1 of the H7N4 virus improves the growth ability while sustaining low pathogenicity. Collectively, the gene composition of the (5 + 3) reassortant virus is a suitable H7N4 CVV for potential pandemic preparedness.

Combating flu in China

China is a major source of avian influenza viruses (AIVs) with bird-to-human transmissibility. Thus, understanding these viruses and treating infections at their source should decrease spread of AIVs to other countries in the world. This special issue focuses on the molecular epidemiology and pathogenesis of influenza viruses, and provides results on current efforts to develop vaccines against AIVs.