Since the 1918 flu pandemic, there have been three flu pandemics – H2N2 in 1956-7, H3N2 in 1968 and H1N1 in 2009 – and before COVID-19 many scientists were predicting that the next pandemic would be caused by a flu virus. If that happens, vaccines will be critical in preventing the spread, yet while we do have vaccines against two bird flu viruses, they will be difficult to scale up should we need them.
The influenza viruses that infect birds are influenza A viruses. Five subtypes are known to have caused human infections: H5, H6, H7, H9, and H10 viruses. In particular, A(H5N1) and A(H7N9) viruses have caused the majority of avian influenza virus infections reported in people, with HPAI A(H5N6) and LPAI A(H9N2) viruses also causing human infections in recent years. In 2021, H5N8 infected people for the first time in a poultry farm in Russia.
In general, bird flu doesn’t infect people easily – the virus binds to receptors in the upper airways of birds that are not as common in mammalian upper airways, which means it is much harder for infected mammals to spread it. Those affected tend to have been in close contact with the animals, such as farm workers, and it doesn’t easily spread between people.
