Ross Clark Ross Clark

Should we be worried by declining Covid antibodies?

(Photo by Simon Dawson – Pool/Getty Images)

Imperial College’s latest React study — an attempt to measure the spread of Covid by testing the general population — suggesting that the number of people in Britain carrying antibodies for the SARS-CoV-2 virus has dropped sharply over the past three months. This led a few headline-writers to run somewhat ahead of the facts. ‘Covid immunity only lasts a few months,’ claimed one. The reality is a lot more complex — indeed, one of the possible interpretations of the Imperial study is that more people have some level of immunity than has previously been believed.

The React study tested 365,000 adults between late June and September, using a self-administered finger prick test to detect for the presence of antibodies. It was a binary test: it did not record the levels of antibodies in the volunteers’ blood — it gave a ‘positive’ response when antibodies reached a certain level and a negative response otherwise. In late June, found the researchers, 6 per cent of the randomised sample had antibodies (with a margin of error of 5.8 per cent to 6.1 per cent). Yet by September, this had fallen to 4.4 per cent (4.3 per cent to 4.5 per cent). The decline in proportion of people carrying antibodies was especially large among the over-75s but much less pronounced among 18 to 24-year-olds. Children were not included in the study.

If antibodies were our only defence, surely we would be seeing vast numbers of reinfections?

The findings led the authors to comment: ‘These data suggest the possibility of decreasing population immunity and increasing risk of reinfection as detectable antibodies decline in the population.’ It is only a ‘possibility’ because antibodies are not the be-all and end-all of the human body’s immune system. Antibodies are the first line of defence against a virus because they prevent it from getting into our cells.

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