Mass vaccination and reduced prevalence of LP H7N9 in China
A new study investigates the evolutionary dynamics of H7N9 avian influenza viruses, particularly focusing on the differences between low-pathogenic (LP) and highly pathogenic (HP) strains in the context of vaccination efforts in China. The study found that LP H7N9 viruses underwent conserved evolution since 2016, resulting in limited genetic diversity and low fitness. This lack of significant adaptive mutations made them more susceptible to elimination through vaccination. The introduction of a recombinant bivalent H5/H7 vaccine (H5N1 Re-8 and H7N9 Re-1) in 2017 was a strategic response to widespread outbreaks of H7N9. The vaccination campaign significantly reduced the prevalence of LP H7N9 in poultry and associated zoonotic infections in humans, demonstrating the effectiveness of targeted vaccination strategies. The research highlighted a strong correlation between the implementation of mass vaccination campaigns and the decline in LP H7N9 prevalence.
In contrast, HP H7N9 strains continued to circulate and evolve rapidly, often escaping the effects of vaccination. The mechanisms behind the disappearance of LP and the persistence of HP H7N9 AIVs remain unclear. The sustained circulating HP H7N9 AIV in North China under the same vaccination procedure might be attributed to its rapidly increasing divergence ratio, which may explain why the HP H7N9 virus is still circulating in northern China and evolves rapidly under vaccination. This underscores the need for continuous monitoring and updates to vaccination strategies to address the evolving nature of the virus.
