Immunity to Covid-19 rapidly declines, research shows

Two new studies show that patients who have recovered from coronavirus rapidly lose antibodies, raising questions over how long immunity to the disease lasts and how reliable antibody testing is.

The studies also highlight the importance the development of a vaccine is to controlling the disease.

One study found that 10 per cent of patients hospitalised with Covid-19 in China had undetectable antibodies just weeks after recovering from the disease.

The study, published on the preprint server medRxiv and not yet peer reviewed, screened 1,500 coronavirus patients in Wuhan for antibodies.

They then compared antibody levels with nearly 20,000 members of the general population, 1,600 patients hospitalised for non-Covid-19 reasons and more than 3,800 health workers who the researchers assumed had been exposed to the virus and therefore had developed antibodies.

They found that one in ten patients who had contracted Covid-19 had no antibodies just weeks after recovering from the disease.

They also found that only five per cent of health workers had antibodies, despite the fact many of them had contracted the disease, and only between one and five per cent of the people in other groups had antibodies.

The fact that one in 10 patients lost antibodies so fast and so few health workers developed antibodies showed that “after SARS-CoV-2 infection, people are unlikely to produce long-lasting protective antibodies against this virus”, the researchers concluded.

The other antibody study, published in the journal Nature Medicine, compared two groups of people who contracted the disease in Wanzhou, China in February. They looked at 37 people who had asymptomatic cases of the disease and 37 who had more severe forms.

They found that 40 per cent of people in the asymptomatic group had undetectable levels of antibodies two to three months after the infection, compared to 13 per cent in the group who had a more severe dose of the disease.

Prof Liam Smeeth, professor of clinical epidemiology at the London School of Hygiene and Tropical Medicine, commenting on the Nature Medicine study, said there were “marked reduction” in immunity among people who had symptoms of Covid-19.

“This strongly suggests that immunity may well diminish within months of infection for a substantial proportion of people. We need larger studies with longer follow-up in more populations, but these findings do suggest that we cannot rely on people having had proven infections nor on antibody testing as strong evidence of long term immunity.”

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