Should we be concerned about the latest React study, which claims that the fall-off in new infections began to plateau from the middle of March? The latest instalment of the monthly study, led by Imperial College, tested a randomised sample of 140,000 volunteers between 11 and 30 March, each of whom was given a PCR test. While the results showed that incidence of infections had fallen by 60 per cent compared with tests conducted between 4 and 23 February, the researchers say that their data shows a flattening-off from mid March.
That is interesting because data from the Public health England test and trace system shows a similar pattern: steep falls in new infections during February, followed by a flattening-off in March. For a few days the seven-day average was going in the wrong direction, leading to fears that Britain could be following other European countries towards a third wave. In the case of the PHE figures, however, there was complicating factor – there was a massive increase in testing from 8 March onwards, as schools returned and pupils and teachers alike were asked to test themselves twice a week for the virus. That posed the question: was the flattening off in new infections real, or was it just a statistical quirk caused by the extra tests picking up asymptomatic cases which would otherwise have gone undiscovered?
The React study suggests that the levelling off in the downward curve of new cases was indeed genuine. As it is based on a randomised sample, it is not affected by a sudden increase in testing. However, the React study also lags behind the PHE figures somewhat, in that it only goes up to 30 March. And the PHE study suggests that new infections have now reimbarked on a renewed, and strong downward trend. Thursday’s figures showed a 36.6 per cent fall in the seven-day average. The figures show that the downwards trend began around 27 March – too late, in other words, to be picked up by React.
Indeed, the PHE daily new infection figures are now falling faster than they were at any point in January and February. That, after all, is what might be expected given that antibody levels show that Britain is now close to the theoretical point of herd immunity.
At that point it ought to be impossible for the epidemic to grow, even if we returned to normal life. Quite why infections plateaued in March is not clear. The return of schools is an obvious factor. There was a similar plateauing in the infection figures in the middle of February, which may have been related to the very cold spell then. But reading the React study in conjunction with PHE figures, there is little in the data to suggest that Britain is about to suffer an upsurge in the virus.
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