Sharp drop...

U.K study finds sharp drop in COVID-19 antibodies just months after infection

Mike Moffitt

One of the vexing things about coronaviruses like the common cold is that the immune response they induce is often short-lived. You catch a cold, recover and then catch it again six months later.

New research published Tuesday indicates fading immunity might also occur with the much more serious coronavirus, SARS CoV-2. Imperial College London scientists found that in a random sample of 365,000 adults in the United Kingdom, the presence of COVID-19 antibodies declined in all age groups by 26% from June to September.

The subjects in the REACT2 study, which has not been peer-reviewed, were given finger-prick tests in three rounds over the summer. After the first round, which ended in July, about 60 of 1,000 people in the sample, or 6%, had positive antibodies. By the end of September, that number had fallen to 44 per 1,000 (4.4%).

Age appeared to affect antibody duration. Younger people had higher levels than those over 65, and their antibodies lasted longer.

A faster decline in antibodies was observed in asymptomatic or mildly symptomatic cases than in those with full-blown symptoms, said Professor Wendy Barclay, head of the college’s infectious disease department, in a video call with journalists. Health care workers showed no change in antibody levels, possibly due to continuous on-the-job exposure to the virus.

“On the balance of evidence, I would say, with what we know for other coronaviruses, it would look as if immunity declines away at the same rate as antibodies decline away, and that this is an indication of waning immunity at the population level,” Barclay added.

“We don’t yet know what level of antibody is needed in a person’s blood to prevent reinfection,” she added.

Just a handful of cases of people getting COVID-19 twice have been confirmed. But immunity from the first wave of infections in March and April may only now be starting to dissipate, raising the prospect of more repeat cases, according to epidemiologists.

The findings suggest that those expecting increased infections to result in so-called herd immunity over time could be disappointed.

Herd immunity occurs when enough of a population is immune to a disease, making it unlikely to spread and protecting the rest of the community.

If no vaccine is developed, the portion of the population that would have to recover from COVID-19 in order to achieve herd immunity is estimated at about 70%, or more than 200 million people in the United States, according to the Mayo Clinic.