There’s more evidence that people start to lose any immunity to the novel coronavirus within a few weeks after they have been infected – especially if they have mild symptoms or no symptoms.
A team at the University of California Los Angeles did an in-depth study of 34 people who had recovered from mild coronavirus infections. They tested their blood two or three times over three months.
They found a rapid drop in antibodies – the immune system proteins that help stop viruses from infecting cells in the body. On average, the antibody levels fell by half every 36 days, Dr. Otto Yang of UCLA’s Geffen School of Medicine and colleagues reported in The New England Journal of Medicine.
A survey of people in Spain released earlier this month found similar results.
“Our findings raise concern that humoral immunity against SARS-CoV-2 may not be long lasting in persons with mild illness, who compose the majority of persons with Covid-19,” Yang and colleagues wrote.
“It is difficult to extrapolate beyond our observation period of approximately 90 days because it is likely that the decay will decelerate. Still, the results call for caution regarding antibody-based ‘immunity passports,’ herd immunity, and perhaps vaccine durability, especially in light of short-lived immunity against common human coronaviruses.”
It’s still not known if people can be infected more than once with the novel coronavirus. But there are other, related coronaviruses that cause common colds, and people can and do catch those repeatedly.
“A crucial question is the extent to which these mildly infected individuals contribute to onward transmission. Another one, is whether or not a mildly infected individual, if infected again, is any more or less likely than average to develop a severe infection the second time around,” said Rowland Kao, an epidemiologist at the University of Edinburgh in the UK who was not involved in the study.
CORRECTION: This post has been updated to indicate that on average, antibody levels fell by half every 36 days.