COVID vaccine debate continues over one jab or two

One of the world’s leading experts has said the benefits of vaccinating more people with a single dose of the COVID vaccine will deliver more benefits in fighting the spread of the disease than providing two doses to a smaller number of the population.

Prof Stephen Evans, Professor of Pharmacoepidemiology, at the London School of Hygiene & Tropical Medicine, has stepped into the ongoing debate of the efficacy of the first dose of the vaccines.

The debate has centred on the level of protection the first dose of the vaccines which have been authorised will deliver and how long that protection will last.

“This is not a simple problem,” said Prof Evans. “The idea that there is a definite clear-cut answer is not true because respected scientists differ in their views.

“In an ideal world, decisions about treatments would only be made within the exact parameters of the trials which have been conducted. In the real world, this is never so.

“It is safest and most cautious to use the vaccines in the exact conditions reflecting the trials. However, this will never be possible in the real world and the question is how much moving outside the exact conditions is acceptable. Pharmaceutical companies are constrained by law and must only make claims that are reflected in the authorisation documents set out by regulatory authorities. Clinicians and health authorities have to take the circumstances they are dealing with into account.

“We have a crisis situation in the UK with a new variant spreading rapidly, and as has become clear to everyone during 2020, delays cost lives.”

He added the speed with which the vaccines have been produced comes with a natural lack of information as to the length and scale of their efficacy.

“The trials did not compare different dose spacing or compare one versus two doses, so we simply do not know what is ‘optimal’. So, the information directly from the trials is lacking,” explained Prof Evans. “We have to utilise what we know from science generally. We know that vaccinating only half of a vulnerable population will lead to a notable increase in cases of COVID, with all which that entails including deaths. When resources of doses and people to vaccinate are limited, then vaccinating more people with potentially less efficacy is demonstrably better than a fuller efficacy in only half.

“It is clearly on stronger ground to use the vaccine in exactly the same way as it was used in the trials, but it is simply not true to say that there is evidence that using the vaccines in a different way will have dramatically reduced efficacy. We have some evidence that the efficacy is quite good, and there are no reasons to believe it will show a sudden decline between three and twelve weeks.

“We must take into account that in the current UK context there will be many more cases of disease and therefore more deaths by vaccinating fewer people.”

However, he said the process adopted by the United States comes in some ways with risk.

“The US is a different environment and sticking to the exact form of dosing used in the trials is more cautious but is almost undoubtedly at a high cost in terms of extra illness and deaths. The US may prefer the certainty of efficacy in half the relevant population leaving half unprotected, for that is the choice in the situation of limited doses and other resources. They may also not have a situation of limits on doses. Giving what may be a higher protection to the highest risk groups could be a better strategy in some circumstances, but it may not be – it depends on the context.

“The key question is how many extra cases (and possibly also deaths) arise through the various different plausible assumptions? Does following the licensed dosing interval lead to fewer cases?

“It is vital to realise that vaccine efficacy (VE) is not a value that applies to each individual – it is an average across individuals, some of whom are essentially fully protected, and some of whom have little protection. A booster will increase the proportion with full protection. Getting the second dose later will probably result in better longer-term protection.”

Prof Evans concluded: “There is no doubt that the UK’s current advice is focussed on public health. The notion that getting one dose results only in protection for 21 days or one month is not biologically plausible.

“What is definitely true is that the UK is uniquely placed to follow-up all those vaccinated and to see if the policy is justified based on the cases of disease among those vaccinated. Data on this will become available within about a month, and policy will no doubt be changed if the data indicate it should be.”

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