H5N1 outbreak: Monitoring the risk to human health

By Professor Stuart Berzins

Australia is now one of few places in the world that is not directly affected by the latest outbreak of the deadly H5N1 avian influenza virus.

Mild forms of H5N1 circulate naturally among wild bird flocks, but pathogenic variants periodically emerge that are highly infectious and cause infected birds to become seriously ill.

The latest important variant to emerge has killed millions of migratory sea birds, shore birds, and waterfowl, including gulls, geese, terns, pelicans, and penguins. Federation University researcher Dr Meagan Dewar recently visited Antarctica and reported four new outbreaks of the virus in skuas, highlighting the geographical reach of this variant and raising concern that entire colonies may be wiped out.

The virus is also carried by other bird species, including eagles, ducks and owls, so it becomes almost impossible to prevent flocks of farmed birds from becoming infected through contact with wild birds or their infected droppings. This can result in huge economic losses because infected birds become unwell and die and farmers usually need to kill the entire flock to prevent the virus from spreading.

Indeed, an egg farm in regional Victoria recently culled hundreds of thousands of birds to prevent the spread of a different variant of avian flu that had caused the death of some of its birds.

A growing concern is the extent to which this variant has become infectious to mammals. Cows, goats, pigs wild foxes, bears and even seals have all been infected, although fortunately, this H5N1 outbreak is not spreading easily to humans. Small numbers of people have been infected in parts of Asia, Europe, and, more recently, the United States, but these have typically been farmers with very high exposure to infected livestock. Several deaths have resulted, but there are no confirmed cases of human-human transmission.

Public health officials are confident there is no significant threat to the community from this current variant, but they continue to monitor the spread of the virus because the mortality rate of previous H5N1 outbreaks in humans has been about 50 per cent.

The chance of the virus undergoing further mutations that allow it to infect and spread between humans remains remote, but newly mutated viruses are always emerging and it is a concern that the latest circulating H5N1 variants have now acquired the ability to infect some mammals.

Given the current outbreak of H5N1 avian flu has been raging throughout the rest of the world since 2020, it seems highly likely that this variant will eventually reach us through migratory birds or imported goods.

To minimise the risk to human health, farms and wild bird colonies are carefully monitored and sick or dying animals are tested for the presence of the virus. A human vaccine for H5N1 is available, but the reserve stocks are low, and as per the annual vaccine taken for seasonal human flu variants, the design of an effective vaccine would need to be adjusted to reflect the structure of the infectious variant, should it ever emerge.

Ironically, our influenza vaccines are currently produced in chicken eggs, so the very process of vaccine production is somewhat threatened by avian flu.

One fortunate outcome of the COVID-19 pandemic was the rapid development of highly effective mRNA vaccines, and the hope is that this technology can now be applied to rapidly develop vaccines that protect people against H5N1 variants and potentially against all forms of influenza.

Stuart Berzins is Professor of Immunology at Federation University.

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