How can you get COVID after vaccination?

It seems likely that the new coronavirus will continue to circulate for the foreseeable future, despite vaccination. So why are we seeing a situation where, despite vaccination, or even having caught the virus, people remain vulnerable to infection? Adam Murphy spoke to Peter Openshaw, an immunologist at Imperial College London, to find out...

Peter – It's a war between the immune system and the virus, and other viruses breakthrough having infected previously and having induced an immune response. A virus I've been working on for about 30 years called respiratory syncytial virus causes bronchiolitis, but it can still reinfect people throughout their lives, even though 96 of people have been infected by the age of three. So it's not that unusual. The one thing the immune system does is remember, the other thing it does is forget if it's not repeatedly reminded.

Adam – And that's just post vaccination with COVID-19. Can we expect it to keep happening, that more and more people become more susceptible as time goes on?

Peter – It's likely that people will become repeatedly boosted and will accumulate some pretty good immune responses over time. If we think that most of the common cold Corona viruses infect during childhood, and that is typically quite a mild infection - it just causes a bit of a common cold - and then when people are re-exposed in later life, they don't typically get very severe disease, because they've already got that immunological memory, which has been built up from that childhood exposure. This game of developing memory and maintaining or losing it is just a lifelong feature of our immune system.

Adam – Do you think we can see that sort of thing happening with COVID? That is, we will become susceptible again, but it won't be the same thing - it'll be something more cold-like than COVID.

Peter – That's what we think is probably happening, yes. This is the first time we've actually been able to watch a virus like this evolve in real time using all the tools that we have at our disposal in terms of modern immunology. It's actually quite an exciting time for immunologists and virologists to be watching all of this actually playing out - there's been a revolution really in our understanding of the immune system.

Adam – How does this work between patient groups, for example in old people versus young people or in people whose immune systems don't work as well? Do they get the same sort of benefits long term, or I suppose fewer detriments than benefits?

Peter – Yes. Well, there are people with weakened immune systems, either because they've got chronic disease or because they're on drugs that suppress the immune system, particularly people who've had transplants, who've had cancer chemotherapy - they won't develop such a good immune memory because immune memory depends on forming new cells. And if those are not being formed, because somebody is on chemotherapy, then immune memory won't develop. There's actually quite a large number of people who suffer from chronic illness, who won't develop such good immune memory. And during old age establishing good immune memory is also sometimes not so secure. So we may need to revaccinate people in order to boost their immune responses, and also maybe direct the immune response into the lining of the nose and lung, which is where we really need it. Of course, vaccines induce very good antibody in the bloodstream, but don't really inform the immune system that where it needs to focus is in the lining of the nose and lung.

Adam – You were talking there about who to vaccinate next. There's been that sort of tension between the joint committee for vaccination and immunisation (JCVI) and the government on whether we vaccinate 12 to 15 year olds or older children with health problems? Where would you fall in that line?

Peter – I think the JCVI are absolutely right to be focusing on those who will most benefit from vaccination. But remember that the brief that they've been given is really to consider the benefit to the individual, not the wider public health implications, or say, the priority that there is to get kids back into school and to try to reduce the circulation of virus in schools, because that will result in school absentees, both for the children and for the staff. So it's not part of the remit of the JCVI to consider that, and I think it's very important to appreciate that when they have made their judgment it's based really on the proven facts in relation to the individual benefit. They are quite reasonably concerned about these reports of inflammation of the heart, the myocarditis or pericarditis inflammation around the heart, which is very, very rare indeed, and actually reasonably common after COVID infection. It seems that that inflammation is probably related somehow to the actual spike protein. It's pretty mild and self-limiting actually after vaccination - I would be much more concerned that it may be more long lasting and severe if we just let the infection rip through teenagers.