Is it possible to get COVID-19 multiple times?

How long does immunity last?

The immune system’s memory is rather like our own – it remembers some infections clearly, but has a habit of forgetting others.

Measles is highly memorable – one bout should give lifelong immunity (as the weakened version in the MMR vaccine does). However, there are many others that are pretty forgettable. Children can get RSV (respiratory syncytial virus) multiple times in the same winter.

The new coronavirus, Sars-CoV-2, has not been around long enough to know how long immunity lasts, but there are six other human coronaviruses that can give a clue.

Four produce the symptoms of the common cold and immunity is short-lived. Studies showed some patients could be re-infected within a year.

Research at King’s College London also suggested levels of antibodies that kill coronavirus waned over the three-month study.

But even if antibodies disappear, then the cells that manufacture them, called B cells, may still be around. B cells for Spanish Flu have been found in people 90 years after that pandemic.

If the same is true with Covid, then a second infection would be milder than the first.

It is also not understood what happens to T cells in the long term. But T cells against the original Sars (Severe Acute Respiratory Syndrome) have been found 17 years later.