At the beginning of the year, Boris Johnson and his advisers were at pains to tell us that by spring we would be in a vastly better situation with Covid. Well, spring is here, the number of new infections and deaths is falling by around 30 per cent week on week, deaths are back to where they were last October and new infections last September. The vaccine programme is running on time, and take-up has been high. Why, then, was the chief medical officer Chris Whitty so downbeat when he addressed the House of Commons science and technology committee this morning?

He told MPs that he was expecting a further surge of Covid ‘with significant numbers but much fewer deaths’ either in the summer or next autumn or winter — with the likelihood that, given the seasonality of the virus, that it would be the latter. Significant numbers of people will still be vulnerable, he said, either because they couldn’t have the vaccine or because they had refused it. He did, however, decline to back the figures in a paper published last month by the government’s modelling committee SPI-M, which presented scenarios in which a further 33,200 to 81,200 deaths between 12 February 2021 and 30 June 2022. Asked by Labour MP Graham Stringer about that scenario, he said that focussing on numbers was ‘unhelpful’.

Yet there are some very tough questions that need to be asked on the scientific advisers. Whatever happened to herd immunity? This time last year Whitty and Sir Patrick Vallance were telling us that the epidemic would not fade away until around 60 per cent of the population had been infected (or immunised, though no vaccine existed at that point).

The US Centers for Disease Control recently revised this up to 85 per cent if the newer, more transmissible Kent variant became the dominant strain. But with the vaccine take-up rate so far reported to be over 90 per cent, and with real-life studies showing that even a single dose of either the AstraZeneca or Pfizer vaccines are 80 per cent effective at preventing hospitalisations among the over-80s, it is hard to reconcile how a fully-vaccinated Britain could suffer a devastating third wave. Whitty and Vallance referred to ‘modelling’ but have not satisfactorily explained to the public their working, and why previous predictions for herd immunity are invalid.

There has at least been some good news this morning: Pfizer announced that its vaccine has shown itself — in the laboratory at least — to neutralise the Brazilian strain of the virus, B1, which seems to have been behind a devastating second wave in the Amazonian city of Manaus. Published in the New England Journal of Medicine, this was only a serological study in the laboratory, and it covers only the Pfizer, not the AstraZeneca, vaccine. But it ought to lay to rest fears that B1 is capable of evading existing vaccines altogether.