Could bird flu be the next pandemic?

What has to happen for bird flu to make it transmissible between humans?
14 February 2023

Interview with

Wendy Barclay, Imperial College London


A mink


A major concern about the present bird flu outbreak is the potential for the virus to jump into humans and - because no one has immunity to bird forms of the virus, the disease can spread very rapidly, like Covid, triggering a pandemic. Those fears intensified recently when scientists reported outbreaks of the virus among farmed mink in Spain, and last week the UKHSA reported detecting the virus in British wildlife, including in mammals like foxes. There were claims that the virus had also mutated to make spread in these animals more efficient. With us to unpick this is virologist Wendy Barclay from Imperial College, London.

Chris - Is the virus showing signs of taking a step closer to us with these recent infections in mammalian species?

Wendy - Yes it is. What we have to understand is that the adaptation of a bird flu to be human to human transmissible requires two different genetic changes, two different changes. So Ian was talking there about adaptations that have been seen. And it's fair to say that both in the foxes and in the mink in Spain, one type of the sort of change, which is the prelude to the pandemic has been seen. And that is an enabler. That is the adaptation that allows the virus to actually replicate inside the cells of the mammals. That's why you get quite a lot of severe disease in those cases, and you can see a lot of viruses accumulating. But the good news is that we have not yet seen the second change, which is the real tough barrier, if you like, for the virus to cross. And that is a change which helps the virus transmit through the air from one mammal to the next or from one person to the next. That change occurs in a different part of the virus in the outside of the virus, in the way it latches onto cells in order to infect us in the first place, and also the way it can be carried in airborne droplets. And so what everybody needs to look out for at the moment are those second types of changes, which are really difficult for the virus to achieve. But if it does, then that's quite a big game changer.

Chris - Many people argue that this is often a numbers game and that this constitutes a role of the genetic dice. And the more roles of the genetic dice, the more likely it is to happen with this scale of bird flu infestation among birds, and now getting into wildlife that is nature rolling that dice. So does this mean that really, the odds have risen that we are gonna see those very changes that you are talking about?

Wendy - You're absolutely right that it is a numbers game and the more exposures and the more incursions of the bird virus into mammals, the more chances that this could happen that risk goes up and up. The one that we are really concerned about, I think, is the mink farm. Because actually your listeners may know that we use ferrets as a model for human flu because the way the virus moves from one ferret to the next is very much the same way that it would move from a person to the next. And of course, ferrets are very closely related to mink, and we believe that the same kinds of barriers would exist there. So the fact that the virus has been in that situation is on the one hand extremely worrying. But on the other hand, the fact that it didn't evolve any of those adaptive changes, even though it was clearly in a situation where the selective pressures may have been acting, might be telling us that the genetic barriers that the virus needs for this adaptation are pretty high.

Chris - Some people argue that because the virus has had 30 years nigh on to do that, having emerged in the 1990s and it still hasn't done it. Perhaps the odds are that it's an insurmountable barrier for it and we don't need to worry.

Wendy - Yes. And that's sort of partly what I was implying. It's been given this opportunity, if you like, in this mink farm situation, and it hasn't done it, but it's very difficult, isn't it, to be confident about something that hasn't happened and say, well, it's not going to. And as you've said before, the frequency of exposures and the opportunities that the virus currently has in terms of the numbers of birds and the interface between those birds and mammals and humans is at a very high level at the moment. So I think we are right to be on an alert system.

克里斯说的,我们能做什么来mitigate it? Obviously there's the surveillance side of it, which Ian was referring to, but in terms of being prepared for if this does jump into people, do we have vaccines? Are they relatively easy to make against this virus? Will they work against this virus? Where do we stand on that?

Wendy - Back in the early 2000s when this H5N1was first becoming a problem and a bigger and bigger worry, a lot of testing was done on H5 vaccines and how they would or could be used. And one of the things we did learn from that is that it actually is quite difficult to get people to make a good immune response to a completely new avian influenza. We give people seasonal flu vaccines every year and we know how to make those vaccines work pretty well. But the avian flu was a little bit more difficult. Because it was brand new the immune system needed a bigger kickstart, if you like, and people talked about using adjuvants, et cetera. I think where we are in a different position today is that we do have, as Louise Moncla mentioned earlier, mRNA. And so the concept of going very quickly from a sequence to a vaccine is the case, but we still don't really know how those mRNAs would work in people against the completely new avian virus, if you like. And I think it would be wise to start thinking about that though.


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