Meeting the challenges of the next flu season

#TogetherAgainstFlu - 29/04/21

An interview with Dr. John McCauley, Director of the Worldwide Influenza Centre, the Francis Crick Institute.

  • The current low level of flu activity has not been seen since the end of the 19th century.
  • It is likely contributing to the waning of population immunity against flu.
  • We don’t know what viruses are like now and if the flu has a better chance.
  • A new virus could emerge; the answer is yet unknown.
  • We should observe what is happening in the southern hemisphere.
  • And observe what is happening in countries combining influenza and coronavirus vaccinations.
  • This should illuminate policies for the higher population density in the northern hemisphere.

With improved COVID-19 vaccination rates and the reduction in the circulation of SARS-CoV-2 the potential lifting of physical distancing measures are likely, and this raises concerns that influenza viruses may increase again. In response to this, Dr. John McCauley talks about what he sees are the challenges for the Northern Hemisphere’s flu vaccination season in 2021, his perspective on vaccinating people beyond risk groups, and how we might achieve higher vaccination rates.

Much of Dr John McCauley’s work at the Francis Crick Institute is directed towards monitoring changes in the characteristics of viruses which are received from WHO National Influenza Centres from across the globe. As well as collaborating on the development of WHO recommendations for the composition of seasonal influenza vaccines and for candidate vaccine viruses against novel zoonotic influenza viruses. John’s broad research interests in influenza are reflected in the many recent publications he has co-authored.

What do you think are the challenges for the northern hemisphere’s flu vaccination season in 2021?

John: Last winter – that is the 2019/2020 northern hemisphere influenza season – was quite typical. But in March, the number of cases dropped dramatically in most countries. I believe this is due to the sudden steep drop at the end of the season which had a double effect: coming to the end of the season and refocusing priorities onto coronavirus.

But within the southern hemisphere, from March till May, we saw that the flu season started taking off and then stopped. The well-resourced countries, particularly the countries that had low coronavirus activity, for example, Australia and New Zealand, did not see a typical influenza season.

We didn’t know what was going to happen. However, some countries started an enhanced flu vaccination program which meant trying to reduce the likely impact of co-circulation of SARS-CoV-2 and influenza viruses. If you have something avoidable, such as flu, you can reduce the risk by extending vaccination programs, and so that was done.

Already, plans have had to be put in place for the coming season because influenza vaccines need to be purchased 10 or 11 months ahead of being deployed. I don’t know specific purchasing plans for countries, but it would seem sensible that the same risk will occur in the 2021/2022 northern hemisphere winter flu season.

That is just planning, but on the virological side, without flu in circulation, population immunity to flu is probably waning. We have had so little flu around that, overall, the population is losing its immunity because immunity drops over time.

That poses two problems:

First of all, we don’t know what viruses will be like now. We have seen flu circulating in a few parts of the world, but we need to find out if these viruses are going to dominate and if they have a better chance of doing this because of limited population immunity.

Or, it might be that a new virus could come out. We just don’t know.

And if we think back, we haven’t seen this low level of flu activity any winter since towards the end of the 19th century. So, we don’t know at this point what to expect. However, what we do know, is we may now be more exposed to zoonotic infections, that’s human infections from animal influenza viruses. I don’t just mean the bird flu H5N1, H5N8 or H7N9, but also swine influenza viruses.

These viruses have not stopped going around within the bird populations or within the pig populations. So, we may be more at risk as population immunity has dropped, meaning we are not only more susceptible to new influenza viruses from humans but also influenza viruses from animals.

What is important now when talking about influenza? With this low immunity overall, should we vaccinate people beyond risk groups? What implications might we see?

John: I would think that, even despite this increased risk of lower population immunity, you still have the threat of having two nasty viruses co-circulating at the same time, influenza viruses and SARS-CoV-2, with similar disease signs and causing death.

So, even if you’re not getting a new virus – for example, it’s just a derivative of an old one, you still, from a public health perspective, need to ensure you don’t have these two respiratory infections going on at the same time. It will be bad enough with SARS-CoV-2 next winter, let alone having flu on top of it.

You can intervene on both and vaccinate for SARS-CoV-2 and flu. But if you look at the stress levels that the hospital system has gone through over the last 14 months, it would be sensible planning to enhance flu vaccinations and encourage more people to get the flu vaccine for this year and next.

In your opinion, should we take a proactive approach to enhance vaccinations?

John: Until you know what is going to happen to coronavirus next winter, there should be measures to ensure that the impact of flu and coronavirus is limited. If they both come up at the same time, health systems could be saturated again.

I understand from our experts on the Editorial Board that research has not indicated that the two vaccines may influence each other; it’s more of a “let’s wait two weeks between the two vaccines”. What’s your view on that?

John: That would be vaccine delivery. I don’t know what the policy would be and work needs to be undertaken on this prior to the rollout of the vaccine for the coming winter.

From what we have discussed with the #TogetherAgainstFlu Editorial Board, two weeks is quite a long time. It’s difficult for some risk groups to keep going back to the hospitals to get immunised, so do you think some research on this is necessary?

John: Work needs to be done on this.. I think countries are going to have to work out their policies and delivery schedules.

Do you have any thoughts on what might happen with influenza and how to achieve high vaccine coverage?

John: We need to observe what is happening in the southern hemisphere, and in the countries that do a lot of influenza vaccinations and, coronavirus vaccinations at the same time. So, observing and examining what’s going on in the southern hemisphere right now, should illuminate policies for the higher population density in the northern hemisphere.

It’s quite feasible that the southern hemisphere will miss two influenza seasons in a row, but I don’t think the northern hemisphere will.

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