Scientists have warned that early adoption of a Covid vaccine with only moderate effectiveness could disrupt efforts to test and create improved versions. Immunising against the disease is not going to be a simple business of turning off the virus once the first vaccine appears, they say. In fact, there could be considerable confusion as researchers struggle to pinpoint the best versions for different vulnerable groups, such as the elderly.

“The vaccines coming through fastest are the most experimental. It is possible they won’t be all that great and that others – created using more tried-and-tested but slower methods – might be better,” said Professor Adam Finn of Bristol University. “But to prove that point will become very difficult if lots of individuals have already been given the first vaccine. It will need vast numbers of people to demonstrate which is best or if a different vaccine is more suitable for particular groups, like the elderly.”

Finn said such confusion could cause setbacks in dealing with Covid, adding: “We should be preparing to meet this challenge and work out ways to compare the effectiveness of early vaccines – but at present we are not doing that well enough.”

A total of 198 Covid vaccines are now under development across the globe with four key versions undergoing final phase 3 trials. These include Pfizer’s BNT162b2 and the Oxford AstraZeneca vaccine.

Results of those trials – in which each is compared with a placebo – are expected in weeks or months. Once the first vaccine that shows efficacy in countering Covid-19 is revealed, there will be enormous pressure to use it immediately. Key candidates would be healthcare workers who deal with Covid cases and others at high risk of becoming infected.

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But for groups such as the elderly, who tend to have weaker immune systems, caution will be required.

“The problem is that early vaccine trials are not likely to show how well these products work in these populations,” said Kanta Subbarao, a World Health Organization director, in an editorial in Nature last week. “We know vaccines often work better in young, healthy adults, which is why they are enhanced with a higher dose or an adjuvant to boost immunity for diseases such as flu and shingles. It is also unclear how well clinical trials will assess effectiveness in those in minority ethnic communities.”

In other words, by spring, several vaccines may have passed their trials without any mechanism being in place to select which is the most effective for different groups. Nor is the problem confined to the UK.

“The complexity and chaos and confusion that will happen in a few short months has hardly dawned on anybody,” Dr Gregory Poland, director of the Vaccine Research Group at the Mayo Clinic, told the New York Times.

It is expected that approval would be given to any vaccine that protects at least half of those injected with it. The problem will come when other vaccines appear and it is unclear whether or not they are better than the first licensed product.

Bryan Deane, a director at the Association of British Pharmaceutical Industry (ABPI), said: “There was a lot of over-optimistic talk earlier this year about Britain having a vaccine before Christmas. However, that really looks unlikely now. Results of trials are not likely to arrive until next year, and when they do they are likely to come out sequentially.

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“The first one that shows any significant protection will be the one people will want to start using straightaway. The problem will be that when the others come through their trials, you won’t be able to say that one is better than another because we have not set up ways to compare them.”

This concern was backed by Finn. “It is a paradox. If we get a vaccine that works, but not very well, it’s almost worse than not having one at all because it gets in the way of getting a better vaccine. We need to be thinking about it to avoid that situation urgently.”



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