There is more evidence that people begin to lose immunity to the new coronavirus within weeks of becoming infected - especially if they have mild symptoms or no symptoms.
A team from the University of California, Los Angeles conducted an in-depth study of 34 people who had recovered from mild coronavirus infection. They tested their blood two or three times in three months.
They found a rapid drop in antibodies - the proteins in the immune system that help prevent viruses from infecting body cells. On average, antibody levels dropped by half every 73 days, reported Dr. Otto Yang of UCLA's Geffen School of Medicine and colleagues in the New England Journal of Medicine.
A survey of people in Spain released earlier this month found similar results.
"Our results raise concerns that humoral immunity to SARS-CoV-2 may not last long in people with mild illness, who make up the majority of people with Covid-19," said wrote Yang and his colleagues.
"It is difficult to extrapolate beyond our observation period of around 90 days because it is likely that the decline will slow down. Still, the results call for caution regarding "immunity passports" based on antibodies, herd immunity and perhaps vaccine durability, especially in light of short-lived immunity to human coronaviruses. common, "says the study.
It is still unclear whether people can be infected more than once with the new coronavirus. But there are other related coronaviruses that cause colds, and people can catch them and do catch them repeatedly.
"A crucial question is to what extent these mildly infected individuals contribute to further transmission. Another question is whether a mildly infected individual, if infected again, is more or less likely than average to develop a serious infection the second time around, "said Rowland Kao, epidemiologist at the University of Edinburgh in the UK. did not participate in the study.
