Should we be worried by declining Covid antibodies?

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.