Just how strong an immunity do Covid patients develop after they have acquired the infection and how long does it last? The question is vital to the likely future passage of the pandemic, and to how well vaccines will protect us in the long term. Several studies have suggested there is a sharp decline in antibodies to SARS-CoV-2 over time – a paper from Imperial College’s React study in October, for example, revealed that the proportion of the population showing antibodies to the virus declined from 6 per cent in June to 4.4