French tests show mild infection protects strongly against coronavirus
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Tests on French health workers with mild forms of coronavirus show that 98 per cent of them developed antibodies powerful enough to neutralise the virus a month later.
The study at two Strasbourg hospitals will help to ease scientific concerns that people with mild forms of the disease do not develop robust immunity to the Sars-Cov-2 virus. The findings also show that the antibody response grows for a few weeks rather than fading immediately after infection.
Olivier Schwartz, head of the virus and immunity unit at the Institut Pasteur and one of the co-authors of the study, said it was too soon to be certain what the results would mean for the long term. But he agreed that the maintenance of protection for more than a month was good news. “Immunity seems to be conserved and even increased, which is really encouraging,” he said.
The research, published as a preprint before peer review, involved 160 health workers who tested positive for infection but did not have serious enough symptoms for admission to hospital. All but one had antibodies against Sars-Cov-2 two weeks after the onset of mild symptoms.
Over the following two to four weeks, the proportion of people with neutralising antibodies — the type associated with protective immunity — rose from 79 per cent to 98 per cent.
Other experts who were not involved in the research gave the findings a cautious welcome.
“We have had a very skewed picture of immunity to this disease so far, with lots of studies on hospital patients,” said Danny Altmann, professor of immunology at Imperial College London. “We have been waiting for studies to come out on people without severe disease, so it is brilliant that this one has appeared.”
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He added: “I find it very reassuring that health workers who did not need to be hospitalised make detectable levels of antibodies. That is positive. But the study has only followed its subjects for a month or so.”
Evidence from other coronaviruses, which may cause serious diseases such as Sars and Mers or mild cold-like symptoms, suggested that initial immune protection would soon disappear, warned Kevin Ariën, professor of virology at the Institute of Tropical Medicine Antwerp.
“Yes, we have good results for a month but we have no way of predicting how long this will last,” he said. “We presume that people infected in this first wave of Covid-19 will be protected if there’s a second wave in the autumn but we don’t really know what will happen.”
Prof Ariën is one of several scientists worldwide planning long-term studies to track the strength of immunity against Sars-Cov-2 over many months. The answers will be important in three ways, he said.
First, they will show whether natural infection in the community will eventually build up a level of “herd immunity” over time. Second, many medical experts are counting on treating patients with antibodies, which may be extracted from the blood of people who have recovered from Covid-19 or made in cell cultures. But they do not yet know how effective or long lasting such therapy will be.
Finally, studies of natural immunity are critical for the development of vaccines to protect against infection, Prof Ariën said.
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