The writer is an English statistician and epidemiologist at the London School of Hygiene and Tropical Medicine

Boris Johnson, the UK prime minister, is right that antibody tests that identify people who have recovered from Covid-19 and can thus return to work will be a game-changer for medical staff dealing with the care crisis. But of itself, detecting who is immune won’t end lockdown — either in the UK or anywhere else.

Most people aren’t immune because they haven’t been infected yet. One alternative is to wait for a vaccine, which will take at least a year, and continue with a severe lockdown. Alternatively, countries can gradually relax lockdowns and let the pandemic run its course slowly, which China and Taiwan have done and the UK seems to be planning.