The science of vaccine spacing

Is spacing COVID vaccines safe?
02 February 2021

Interview with 

Keith Neal, University of Nottingham


A close up of a wall calendar


This week the UK passed the grim milestone of 100,000 COVID fatalities. But on a more positive note, two pharmaceutical companies, Novavax and Janssen, both announced solid phase 3 trial results for their new coronavirus vaccines. And in the UK, 8 million people have now received at least one dose of either the Pfizer or AstraZeneca vaccine. But, apart from recent moves on the part of the EU which could affect supplies of vaccines to countries outside the bloc, many are also concerned about the decision to delay the second doses of their vaccine in order to protect more people in the short term. The British Medical Association have been vocal, calling for an urgent review of the UK’s strategy and saying the gap between the first and second doses should be reduced to 6 weeks. The doctors' union say the UK’s approach is "increasingly isolated internationally" and "is proving difficult to justify". On the contrary, other experts have defended the decision and some have even slapped down the BMA as ill-informed, arguing instead that the delay may even lead to better long-term immunity. Chris Smith asked University of Nottingham infectious disease epidemiologist Keith Neal what he makes of all this, and what, does he think, should be our long-term vaccination plans for COVID-19?

Keith - If you've got 10,000 doses of vaccine, you could give 10,000 people 70% protection. Or you could give 5,000 people 90% protection. That means we protect a lot more people. Also, if the vaccine does interrupt transmission, we would actually stop more transmission chains by doing it this way.

Chris - Do we actually have evidence that it works like that though, because one of the criticisms that people have been levelling at those responsible for making this change is that they are departing from the clinical trial evidence. They're departing from what the manufacturers have initially said should happen and therefore, this is risky.

Keith - The manufacturers are constrained by what they're allowed to say by their own pharmaceutical association. We often give vaccines for viruses naught and six months apart, as for hepatitis A, and the human papilloma virus and they work very well. Having a short period between the two vaccines was really a necessity so that we could get the results of the vaccine trials in quickly. If we had a six month gap, we wouldn't still know what the results were.

Chris - Therefore, are we actually trying to learn, right now, what the answer to this question is? In other words, are there various measures in place to learn from what we are doing, having changed this a little bit to find out whether we are on solid ground by doing this?

Keith - Part of the advantage of a national health service system is that we'll be able to identify anybody who gets COVID after they've had a vaccine. So we'll be able to rapidly identify whether it is or is not working to the degree that we hope it does.

Chris - And is there any evidence emerging yet? Because obviously we've got 6 million people or more now who have had vaccines, so there are a very significant number of people who can be followed.

Keith - I actually haven't seen any of the published data, although I did have one care home where as part of a routine screening an outbreak was identified quite widespread in the home. They'd been vaccinated 10 and 11 days earlier, and none of them had got ill. They were all asymptomatic.

Chris - What's your thoughts on how the rollouts are actually going with the vaccine now and are you encouraged by the sorts of numbers that we're seeing? Do you think this is enough?

Keith - Having been involved in planning mass vaccination campaigns before I'm very encouraged about how far it has gone. Yesterday's figures suggested over one in 11 of the entire population had been done and we're up to three quarters of the over eighties where most of the deaths occur. This is an amazing achievement really from having not had even known about disease really this time last year.

Chris - And looking to the future, obviously we don't know because we don't have a crystal ball. What's going to happen in terms of next winter? Do we have any insights yet about how long the protection is going to last from this vaccine and how were we going to plan for the virus, possibly sidestepping these vaccines? If we continue to get variants and things like that coming along?

Keith - I'd like to think that we can model it on the flu program. We know that the flu virus changes much faster than the Coronaviruses do and simply if we actually have to have a flu and COVID vaccine simultaneously in the winter, then we've got one arm for flu vaccine and the other one for the COVID vaccine. We can actually tweak the COVID vaccine in about six weeks, which is much faster than we can change the flu vaccine. Given now we have a large army of people who trained to give vaccinations. We might have to actually be able to scale up our flu vaccine campaign in general and have a flu COVID vaccine.

Chris - Are you optimistic?

Keith - I'm not pessimistic. I mean, I continue to hear stories of the vaccine won't work, it will come back, the virus will change. Each of those, we are able to defeat and we are learning rapidly about how to do things better. I think what will happen. We need to have better ways of trying to identify Coronavirus in the population and the lateral flow devices will help this and they will. The main name of them is to find people who are asymptomatic so we may be in a position of having regular testing for a while.


Add a comment