By Priya Joi
Currently, the worst ever outbreak of bird flu is causing mass die-offs in poultry and other birds, and is starting to be seen in animals from otters to dolphins. If the virus evolved to be able to spread easily between people, the concern is it could trigger another major global outbreak.
In general, bird flu doesn’t infect people easily [...] However, the fact that the current global H5N1 bird flu outbreak has caused such large die-offs and has started to spread in small mammals means that some scientists are concerned.
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.
Strains of bird flu causing concern
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.
However, the fact that the current global H5N1 bird flu outbreak has caused such large die-offs and has started to spread in small mammals means that some scientists are concerned that the virus could evolve to spread more easily among human beings, potentially triggering another pandemic.
Why not just vaccinate birds?
Vaccinating birds against flu is not easy. In 2017, China began mandatory vaccination of poultry against an H7N9 strain that was able to spread to people, thereby stemming the spread of the virus. But this strain affects fewer varieties of birds, unlike H5N1.
Moreover, public health officials are worried that if vaccination isn't carried out properly, the virus could continue circulate at a low level, actually increasing the chance of mutations and spread to people.
Given the potential threat, the US is to test a vaccine that could be given to poultry in a bid to staunch the spread of the virus.
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