COVID vaccine trials in children and immunocompromised people

In recent weeks the UK government has announced a £7M initiative to look at the potential value of mixing and matching different vaccines. Trials are also underway to look at how well the vaccines perform in children, who were not included initially, and also among people with compromised immune systems. Rajeka Lazarus, from University Hospital Bristol and Weston, is running several of these, and spoke to Chris Smith...

Rajeka - So the main rationale is to improve the flexibility and ease by which the vaccines can be delivered, so that as many people as possible can be vaccinated. So what this means is if you've been vaccinated with one type of vaccine, and you're ready to have your next dose, if your local centre actually doesn't have that, then it's going to be more difficult, or more time consuming for you to get the same dose as you had before. So that's really the main reason. The second reason is that there may be some advantages in having the different types of vaccines. They may compliment each other, and actually enrich the immune response overall.

Chris - Do we have evidence that that's actually the case, because arguably some people who are being recruited into this trial could say, well, actually, that doesn't sound good if you don't know for sure. So I won't take part.

Rajeka - So we do have some evidence so far, that has been found in animal studies, where they have given the different types of vaccines together. And actually it did show by having two different vaccines, you get a richer immune response, and a higher antibody concentration compared to having two of the same vaccine type. So that is promising. And what we're looking for in this study really, is not that the two different vaccines make a better response, it's that they don't make any response that's less than two of the same doses.

Chris - There's also some question about whether or not some of the vaccines that are being used, can be used more than once, because the vaccines are themselves a virus, and this will elicit an immune response on the part of the recipient. And some are arguing this could therefore be a safeguard on the part of our ability to defend the population, because we may have to use different vaccines in people the next time they're vaccinated going forward. So knowing this information up front is very helpful.

Rajeka - Yeah, that's absolutely right. There have been a small number of people who received these viral vector vaccines that you've heard talked about. For other infections, for studies done in Oxford who have been part of the trial, and have found to be, have adequate responses. But we do need more information.

Chris - You're also looking at children now, some may say, why didn't we look at children in the first place? And also if children are at such low risk, which has been the policy headline along the way, children don't seem to get this very severely. They don't seem to pass on the virus very often. Why are we now vaccinating or worried about vaccinating children?

Rajeka - I think it's quite usual practice to test out new vaccines and other products in healthy adults first, and then move on to other groups who may benefit from vaccination. Although children are lower risk, they're not at no risk. And there may be some children who are more vulnerable than others. And we do know that children can get COVID, and they can get post infection syndromes that can make them quite poorly. And it's also thought that, certainly with the new variants, they are transmitted as effectively in all the age groups. So it may be that children are involved in transmitting the virus within the community. So if we do want to stop transmission, we need to look at vaccinating children.

Chris - The other group who are also concerned, are people who have a poorly functioning immune system, the so-called immunocompromised. People who are on drugs that suppress their immune system. People who've had organ transplants, bone marrow transplants. They may have some inherited problem with their immune system, or disease like HIV. So their immune system might be broken for that reason. They haven't been formally studied so far, have they, as a group to see how they respond to the vaccine? So how are you trying to learn what sort of advice we can offer to somebody who's in that situation? They're a bit immunocompromised or a lot immunocompromised, and they'd like to know what their prospects are having had the vaccine.

Rajeka - So that's right Chris. The studies haven't been done in this group of people with problems with their immune system. And I think that the main thing to say is that these vaccines are safe. They're not live vaccines. So they shouldn't cause you any problems if your immune system is compromised, but we still need to establish how well they do work. And there are studies that have been started in the UK to follow-up people with different types of immune system problems, to establish how well they're working, to then work out whether people may need a different type of vaccine, or more doses, and work out how best to protect people with these problems.

Chris - And to finish us up here, Rajeka, what do we know yet about how long the immune response lasts for, in response to these vaccines? Because obviously we don't have time machines. We don't have crystal balls, we can't see into the future. So we really only know a bit about the time since we've been giving the vaccine. So what do we anticipate will be the length of protection, because that will obviously inform what we decide to do next in terms of boosting people and so on.

Rajeka - Yeah. I think that is a difficult question to answer at the moment, but the information is being collected. So the first people to start, certainly in the Oxford vaccine study, started a study last April, May. So we are coming on to close to eight, nine, ten months. So we will have some information. I think it's reassuring that we can see from the Oxford study, that a single dose provides good protection that persists for the 12 weeks. And we know that the booster dose will then produce a higher antibody response, which should then last longer.