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The Oxford Covid jab is delivered this week. But when will vaccines bring results?

Postat la Jan 03, 2021

People in Britain are set to get their first shots of the Oxford/AstraZeneca vaccine on Monday, with millions of doses being given over the next few months. The mass vaccination of the UK’s population should bring an end to the country’s Covid-19 misery, but how long will it take for this immunisation programme to make a difference to our lives – and what will be the first signs that salvation is on the way?

These key issues will be anxiously pursued as the battle against Covid proceeds and daily cases involving the new virus variant continue to spread. However, scientists have warned that simply waiting for a reduction in new cases is not the way to tell whether the vaccine is starting to have an impact.

This point was stressed by Professor Adam Finn of Bristol University. “In February, we may see a big decline in the numbers of cases,” he told the Observer. “That would be good news, but we wouldn’t know whether the drop was due to the vaccine, to lockdown measures or to some other factor.

“Conversely, case numbers may go up in February and March, and you might reach the false conclusion that the vaccine was not working when, in fact, the rise was due to other factors, and the increase in daily cases would have been even higher had we not been vaccinating.

“So just looking at overall trends isn’t going to give us answers in the short term. Obviously, we expect the vaccine to have an effect but we will need to be clever about how we find the first signals that say it is working.”

One project that should provide the first indication that the national vaccination programme is having a beneficial impact is being carried out at Bristol University and involves cases of pneumonia. In a case control study, doctors will compare people who are suffering from pneumonia and test positive for Covid-19 with patients who have pneumonia but test negative for the virus.

A nurse administers a dose of the Pfizer-BioNTech Covid-19 vaccine. Photograph: Sameer Al-Doumy/AFP/Getty Images

“Then we will measure rates of immunisation within those two groups,” said Finn. “That will allow us to calculate just how effective the vaccines are, because you will expect to see that a much bigger proportion of the people falling sick are the ones who are not immunised.

“That will give us, very quickly, an indication of how effective the vaccine is. And finding cases of pneumonia to compare will not be the problem at this time of year. There are always plenty of these in winter.”

The Bristol pneumonia study and other similar trials will provide the first signs that the UK is on the right track and the vaccine is starting to make a difference. The next indication will arrive when numbers of hospitalisations and deaths steadily decline to a level where scientists can be confident that it is a Covid-19 vaccine that is producing real results and that other factors are not involved.

The UK will then know just how effective its immunisation strategy has been. This should resolve a dispute that has led some doctors and scientists – including leading US infectious diseases expert Dr Anthony Fauci – to question the British decision to delay giving second doses of Covid-19 vaccines in order to maximise the numbers of people who could be protected rapidly against the disease.

Fauci told CNN on Friday that while it was possible to “make the argument” for stretching out the doses, he would not be in favour of doing that.

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This view was echoed by Professor Martin Hibberd of the London School of Hygiene and Tropical Medicine, who said: “The science has been of a very high standard for the vaccine trials, and it is highly frustrating that this is now being ignored. We do not know how the vaccine will perform with an increased gap between the injections, and we do not know how protective a single injection is going to be over the longer term. So why take the risk?”

However, Professor Chris Whitty, the chief medical officer for England, along with his counterparts in Wales, Scotland and Northern Ireland, have said they stand by their decision to delay a second dose in order to ensure that more people are able to receive their first as soon as possible.

Why is Britain delaying second doses of Covid vaccines? Read more

And this view was backed by Professor Stephen Evans, also of the London School of Hygiene and Tropical Medicine: “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. When resources of doses and people to administer vaccinations are limited, vaccinating more people with potentially less efficacy is demonstrably better than a fuller efficacy in only half.”