SARS-CoV-2 Antibodies Detected in Around 1 in 7 People in England

Peter Russell

February 25, 2021

High levels of antibodies were detected in people of all ages who received two doses of the Pfizer/BioNTech COVID-19 vaccine, a study preprint has suggested.

Researchers also found high responses to a single dose of the vaccine among those with previous infection from the SARS-CoV-2 virus.

However, the data from round 5 of the REACT-2 study, carried out by Imperial College London (ICL), was insufficient to show the effect of antibody positivity on hospitalisations and deaths.

The study also suggested that confidence in the vaccine was high, but lower in some groups, including key workers and those from ethnic minority backgrounds.

Lateral Flow Antibody Tests

The findings were based on self-testing of more than 155,000 participants in England using finger-prick lateral flow devices between January 26 and February 8.

For the first time, ICL researchers were able to capture the initial impact of the COVID-19 vaccination programme.

There was sufficient data for the effects of the Pfizer/BioNTech vaccine to be registered, but not the impact of the AstraZeneca/Oxford vaccine which started its roll out later.

Of the participants, 18,000 had received at least one dose of vaccine.

Overall, antibody prevalence was 13.9% of those tested. That ranged from 9.8% for the unvaccinated cohort to 37.9 % for participants who had received a vaccine.

Of those who had received two doses of the vaccine, antibody positivity was 88% in the over 80s, rising to 95.5% in people under 60.

Following a single dose of the Pfizer/BioNTech vaccine, 84.1% of people under 60 tested positive for antibodies after 21 days. That figure was highest in those under 30 at 94.7%, declining with age to 73.7% at 60, and 34.7% in the over 80s.

Helen Ward, professor of Public Health at ICL, said: "Our findings suggest that it is very important for people to take up the second dose when it is offered."

Although antibody positivity declined with increasing age, a 90.1% response was noted in vaccine recipients with previous confirmed or suspected COVID-19.

"What we can say from our data is that we do see very good antibody positivity results in people who have had previous COVID after one dose to a point that they're at least as good as people who have had two doses of the Pfizer/BioNTech vaccine," said Graham Cooke, professor of infectious diseases at ICL.

Prof Cooke told a briefing hosted by the Science Media Centre that "people who've had previous infection alone don't seem to have such high levels", demonstrating a "value in getting that first dose in the setting of previous infection".

Antibody prevalence in unvaccinated people was found to vary across the country. The highest rate (16.9%) was seen in London.

Black people were also most likely to test positive at 22.4%, followed by Asian individuals at 20%, compared with 8.5% of White people.

Antibody prevalence also varied by employment, with the highest rates found in healthcare workers (21.9%) and social care workers (24.2%).

People in public-facing jobs such as police officers and teachers were also more likely to test positive than non-key workers.

Vaccine Confidence

Research conducted in association with pollsters Ipsos MORI found high rates of confidence in the vaccine, with 92% of people saying they had accepted or intended to accept the offer of vaccination.

However, this varied by age and ethnicity.

The lowest confidence levels were seen in young people and those of Black ethnicity.

Particular concerns were seen around pregnancy, fertility, and allergies.

"We know that some groups have concerns about the vaccine, including some people at increased risk from COVID-19, so it is really important that they have opportunities to discuss these and find out more," said Prof Ward.

Expert Reaction to the Study

Commenting on the study, Dr Simon Clarke, associate professor in cellular microbiology at the University of Reading, said: "It is of concern that in studies of individuals aged 70 years or over, a single dose of the vaccine was associated with substantially lower levels of antibodies than in younger age groups, or in those who had had COVID-19 prior to vaccination. 

"This shows that with this vaccine, the immune response is much greater in individuals who have been exposed twice, either through a prior infection or through double vaccination."

Kevin McConway, emeritus professor of applied statistics at The Open University, commented: "This study didn't measure whether people actually got ill, only the antibody response, so it cannot directly tell us about the effect of vaccination on suppressing COVID illness. But the signs are good for people who have had two doses of this vaccine."

Marian Knight, professor of maternal and child population health at the University of Oxford, said: "The large size of the study provides additional reassurance that confidence in the vaccine is high across most population groups. It is, nonetheless, worrying that participants are reporting concerns over planned or current pregnancy and fertility.

"Guidance from the Royal College of Obstetricians and Gynaecologists is clear that women trying to become pregnant do not need to avoid pregnancy after vaccination and women should be reassured that there is no evidence to suggest that COVID-19 vaccines will affect fertility."

REACT-2 Round 5: increasing prevalence of SARS-CoV-2 antibodies demonstrate impact of the second wave and of vaccine roll-out in England, Helen Ward et al. Preprint.

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