Did Covid lockdown make us vulnerable to other diseases?

We know that the lockdowns had the intended effect on reducing transmission rates of the SARS-Cov-2 virus that causes COVID-19, but what was the impact on the normal pattern of circulation of other infections, and how did they change in the aftermath? And has this had any effect on our immunity and disease susceptibility as a result, producing, at a population level, what some have labelled an “immunity debt” that has triggered a subsequent surge in disease and even new disease manifestations to appear. In 2022 an alarming spike in children with hepatitis was picked up and subsequently put down to a virological “one-two punch” caused by vulnerable individuals catching multiple bugs in quick succession. Brian Ferguson is an associate professor of innate immunity at the University of Cambridge, and began by outlining what the rationale for the lockdowns was when the pandemic began...

Brian - There was a lot of understanding of a new and lethal virus infection spreading out of China through Europe and towards the UK. And at the time there wasn't any understanding of what really this virus was, why it was lethal. And there weren't any drug treatments or vaccines available at the time. So a lockdown was proposed in order to try to stop people from interacting with each other and therefore to reduce the chances of this new and deadly infection from being able to spread between people. And at the time that was proposed, it was one of the only mechanisms which would have been seen to be effective way of, of stopping this virus from spreading in a way which would buy some time in the population so that scientists could as quickly as possible, develop drug treatments and vaccines that would help to combat the virus.

Chris - Had we ever done anything like that before or was this a completely new manoeuvre?

Brian - In the UK, this is a completely new manoeuvre. It wasn't something that had been tested before at a population level in the whole of the UK.

Chris - And was it effective? Did it actually do what it said on the tin?

Brian - Yes, it did. It did what it said on the tin. So the number of infections went down as lockdown was introduced and that was the idea. So it bought some time for people in the background to start as quickly as possible developing the drug treatments, testing them, developing vaccines, testing them so that they could be introduced later.

Chris - If it stopped or interrupted the circulation of one disease that was SARS-CoV-2 that causes COVID-19. It must have had the same kind of impact on everything that we spread amongst ourselves.

Brian - Yes, that's absolutely true. And we saw that at the time and subsequently by looking back at data where people have counted the number of infections of other respiratory diseases during that period and seen a massive reduction in the whole host of other infectious diseases during that period of time when there was lockdown. And that includes things like influenza, flu virus infections, and RSV, which is respiratory syncytial virus, which causes the disease to be especially nasty for young children. So those virus infections dropped off dramatically during that lockdown period as well.

Chris - Now when we talk about infections like the ones you've just mentioned, there's two considerations. There's the acute effect stopping infections spreading right now, and then there's the longer term seasonal trends. Because if we look at those viruses you've mentioned, they tend to have a season. We have a flu season, we have an RSV season. So notwithstanding what you said about interrupting the acute spread, have there been any repercussions for the long-term seasonal trends we see with those other viruses of these lockdowns?

Brian - That's something that people are still monitoring very carefully. And we have seen immediately in the year after lockdowns, there was an increase in RSV infections that came back through the winter of 2022 and potentially the winter of 2023 in some places, but not others. There may have been an increase in some of those infections as they came back into the population after having been kind of restricted or locked out of circulation of those populations during the period of when we were in lockdowns for SARS-CoV-2.

Chris - Why do you think that is? Why did we see the fact that we get a resurgence but it's higher, it's a bigger bounce back, effectively?

Brian - Yes. I think that's something that genuinely isn't understood very well. It may be that there are people at that time who would've been infected, therefore, were not developing longer term immunity during lockdown. And when they've come back into the population, there are more people who are slightly more susceptible to that infection. That's one option. There are also lots of other potential explanations, which I think are worthy of consideration retrospectively as we gather more data about the exact numbers of those infections over subsequent years. because don't forget, this is not actually that long ago that we went through this process and these seasonal trends of viruses do change all the time, irrespective of the lockdown. So it needs a longer term view in a global way to understand whether there are short, medium, or long-term implications of the circulation of those other viruses impacted by lockdowns due to SARS-CoV-2.

Chris - We also saw possible speculation that lockdowns interrupted the sequence in which, particularly young people, were catching things for the first time, leading to some co-infections occurring with agents that were then having more severe consequences than if they had just caught them at a normal time. What did you make of those hepatitis cases in young people a couple of years ago that was quite dramatic in a number of countries. The UKHSA suggested it might have been down to people catching an adenovirus and something on top of that which was causing a ‘one-two’ punch in susceptible individuals.

Brian - This is another interesting area of research, understanding whether there are specific consequences to having co-infections at the same time. This is people trying to causally link clinical manifestations of clinical infections with the amount of immunity people have, and the amount of co-infections people have at different times. We’re currently at the place where there isn't enough information about that to say for certain whether there are those casualties between circulating infections working together, and then on top of that, weather that was altered during those lockdown periods.