Covid-19: Antibody levels ‘waning quite rapidly’ after infection, new study finds

  • Antibodies appear to decrease rapidly after SARS-CoV-2 infection, a recent study found
  • Asymptomatic individuals involved in the study were also found to quickly lose antibodies 
  • The results stress the need for everyone to continue following preventative measures

Antibodies against SARS-CoV-2, the virus that causes Covid-19, was found to decline rapidly in the British population, a Real-Time Assessment of Community Transmission (REACT) study found.

The study, by Imperial College London and market research firm Ipsos Mori, is one of the largest of its kind in Britain to suggest that neutralising antibodies, which can prevent an infection from taking hold, may only last a few months.

The data included samples from hundreds of thousands of people across England between mid-June and late September.

According to the researchers, the prevalence of virus antibodies fell by more than a quarter during this period. Their findings also suggest the loss of antibodies was slower in 18–24 year-olds compared to those aged 75 and over.

“Our study shows that over time there is a reduction in the proportion of people testing positive for antibodies,” explained Professor Paul Elliott, director of the programme at Imperial.

Their findings have been published in a pre-print report and will be submitted for peer-review.

Tracking antibodies

The researchers tracked antibody levels in 365 000 randomly-selected adults following the first wave of Covid-19 infection in the UK. The analysis was done via finger-prick tests carried out at home between 20 June and 28 September.

They found that antibody prevalence fell by a quarter, from 6% of the study population around June, to a low 4.4% in September.

The decline was also largest in people who didn’t report a history of Covid-19, dropping by almost two-thirds (64.0%) between rounds one and three, compared to a decrease of 22.3% in people who had an infection confirmed by PCR (polymerase chain reaction) testing.

“This very large study has shown that the proportion of people with detectable antibodies is falling over time,” said Professor Helen Ward, one of the lead authors of the study. "Immunity is waning quite rapidly; we're only three months after our first [round of tests] and we're already showing a 26% decline in antibodies.”

Asymptomatic cases

More than this, antibody levels in asymptomatic individuals were also found to be less than those who had displayed symptoms.

“Antibody positivity was greater in those who reported a positive PCR and lower in older people and those with asymptomatic infection.

"These data suggest the possibility of decreasing population immunity and increasing risk of reinfection as detectable antibodies decline in the population,” the authors wrote.

The report also indicates that there was no change in the levels of antibodies seen in healthcare workers, most likely due to repeated exposure to the virus.

Importance of following preventative measures

“Testing positive for antibodies does not mean you are immune to Covid-19. It remains unclear what level of immunity antibodies provide, or for how long this immunity lasts,” explained Elliott, adding:

“If someone tests positive for antibodies, they still need to follow national guidelines including physical distancing measures, getting a swab test if they have symptoms and wearing face coverings where required.”

Health Minister Lord Bethell also commented on the study, saying it is “a critical piece of research, helping us to understand the nature of Covid-19 antibodies over time, and improve our understanding about the virus itself”.

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Image: Getty/mbz-photodesign

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