A strain now circulating in dairy cows appears to carry little risk for humans at present, but we need to develop an effective strategy before it mutates
As usual, I’m back with cheery topics to get us through the dark, cold winter months. No, I’m not talking about the studies on how dark chocolate reduces your risk of type 2 diabetes or why eating cake for breakfast isn’t as bad as we think it is. Instead, in the global health world, the main news is about avian flu, the H5N1 virus, and also the deadly outbreak in the Democratic Republic of the Congo of a mystery illness. It’s in these moments that I wonder why I didn’t choose a career in baking.
But trying to replicate a Mary Berry recipe would require eggs – and the United States is facing a shortage of eggs – like Britain did last year – with the main culprit being avian flu, which has either killed off or triggered the culling of hundreds of thousands of chickens. Avian flu has caused concerns recently given several step-changes in the seriousness of the potential threat: becoming endemic in wild bird populations; then its spread among domestic birds, causing a turkey lockdown in winter 2022; then reports from across the world about infections in mammals such as sea lions that feed on or live near wild birds. In the past year, a big shift has been the confirmation of mammal-to-mammal transmission among dairy cows in the US.
The growing proximity of the virus to humans has resulted in an increasing number of infections in humans in the past year (bird-to-human or cow-to-human), but H5N1 can still not transmit human-to-human the way Sars-Cov-2 or seasonal influenza can, which is why it’s considered low-risk. However, a recent Science article noted that the strain in cows would only require a single mutation to enable the virus to move from avian to human specificity. This is the shift that would trigger governments to activate their pandemic preparedness and response plans and would make it leap to the top of risk registers.
But there are even more puzzles when looking at H5N1. Prior to this year, the death rate was estimated to be about 50%, and it’s still deadly for many species of birds and cats. But out of the 57 confirmed infections in the US in the past year, all have been mild and none hospitalised. Scientists don’t fully understand why, although there are hypotheses: could the strain circulating in dairy cows (and causing human infections in the US) be less dangerous to human health? Or is it about the route of transmission from cows to humans, or some existing immunity in the population? It’s worth contrasting this with a teenager in Canada who was infected with H5N1 from wild birds (a different strain to the one in cows), and was admitted to hospital with severe pneumonia, where he remains on a ventilator.
Looking forward, it wouldn’t be wise to just assume it won’t further mutate or will be a mild strain. If I worked in a government health department, I would be preparing plans for how best to respond to more avian flu cases in humans, including GP and hospital guidance, vaccine and antiviral testing and stockpiling and containment plans.
First, we need to continue to detect cases, which requires a testing strategy and adequate diagnostics. Sequencing positive samples can tell us where someone got infected, the strain they have and how infectious transmission is. Currently, the UK has a detection strategy for high-risk workers and in hospitals. In the first part, samples are taken randomly through nose and throat swabs for those working closely with birds on poultry farms, for example, to identify asymptomatic cases and ensure we’re not having undetected spread. In the second part, NHS hospitals ensure those admitted to intensive care with severe respiratory infections or influenza-like symptoms are tested for avian flu, if seasonal influenza is not found.
We must also prepare medical countermeasures such as vaccines and antivirals such as Tamiflu. We are fortunate to have an approved vaccine, which has been previously used for those working on a mink farm in Finland, and the UK has stockpiled 5m doses. While it’s useful to have a generic H5N1 vaccine ready to go, it wouldn’t be specific to the strain circulating. On an avian flu briefing several months ago, a senior director from the Centers for Disease Control and Prevention noted that the US was waiting to stockpile vaccines so that they could match the circulating strain most precisely, if needed. But producing enough vaccines rapidly would be a problem given that H5N1 vaccines are currently made in eggs, which are dependent on healthy chickens. The US government spends millions of dollars on contracts with poultry companies for eggs, kept ready for vaccine production. These chickens are kept in secret locations and protected by both physical and biosecurity measures to ensure the egg supply is secure. It’s estimated to take at least six months from the arrival of an egg to an approved vaccine, making emergency scale-up tricky.
In addition, we need a clear strategy over the management of spread. If the circulating strain is indeed mild in humans, would officials tolerate spread while vaccinating in high-risk groups? What if it’s more serious in humans, and young people and especially children become seriously ill? What if hospitals become overwhelmed? In this case, what is the plan to contain and delay until vaccination? How do we build trust in yet another vaccination campaign? It’s better to pre-empt these questions and prepare plans that help decision-making in a logistical and balanced fashion.
For now, unless you’re a scientist working in this area, a health or agricultural official, a farm worker or in close proximity to animals, or you consume raw milk or undercook meat (which is a bad idea anyway), it’s not yet a major concern. But if the picture changes further, we won’t be able to avoid the topic. For now, you can get back to your Christmas baking and those precious eggs.
Prof Devi Sridhar is chair of global public health at the University of Edinburgh
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