A new study of people who have caught and recovered from coronavirus raises the prospect that immunity to the virus may be short-lived.
Scientists at King’s College London studied how the body naturally fights off the virus by making antibodies, and how long these last in the weeks and months after recovery.
Almost all of the 96 people in the study had detectable antibodies that could neutralise and stop coronavirus. But levels began to wane over the three months of the study.
How do you become immune to coronavirus?
Our immune system is the body’s defence against infection and it comes in two parts.
The first is always ready to go and leaps into action as soon as any foreign invader is detected in the body. It is known as the innate immune response and includes the release of chemicals that cause inflammation and white blood cells that can destroy infected cells.
But this system is not specific to coronavirus. It will not learn and it will not give you immunity to the coronavirus.
Instead you need the adaptive immune response. This includes cells that produce targeted antibodies that can stick to the virus in order to stop it and T cells that can attack just the cells infected with the virus, called the cellular response.
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 life-long 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.
But the common cold is generally mild. There are two more troublesome coronaviruses – the ones that cause Severe Acute Respiratory Syndrome (Sars) and Middle East Respiratory Syndrome (Mers) – in which antibodies have been detected a few years later.
“The question is not whether you become immune, it’s how long for,” said Paul Hunter, a professor in medicine at the University of East Anglia.
He added: “It almost certainly will not last for life.
“Based on antibody studies in Sars it is possible that immunity will only last about one to two years, though this is not yet known for certain.”
However, even if you are not completely immune it is possible a second infection would not be as severe
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