96% of Britons develop antibodies after one Covid jab, study finds

More than 90% of Britons develop antibodies to coronavirus after having one dose of the AstraZeneca or Pfizer vaccines, and almost 100% do so after their second jab, research shows.

The findings, based on a study of 8,517 people in England and Wales, are the latest evidence to show that the two mainstays of Britain’s vaccine drive are proving highly effective.

The research found that 96.42% of people who had either vaccine had developed antibodies 28 to 34 days after their first dose. That rose to 99.08% within seven to 14 days of the second jab.

Both vaccines were equally good at triggering the antibodies needed to fight off Covid-19, the researchers from University College London (UCL) found.

“This is one of the earliest real-world vaccine studies in the UK and it is fantastic news”, said Dr Maddie Shrotri, the lead author of the paper containing the findings.

“Over nine out of 10 adults in the UK who had either the Pfizer or AstraZeneca vaccine produced antibodies against the virus within a month of their first shot.

“How well these vaccines work is remarkable, especially given the speed at which they’ve been developed. It’s a real feat of science in the face of the most devastating pandemic in a century.”

The conclusions are based on analysis of 13,232 antibody samples given by the 8,517 adult participants in the trial, none of whom had antibodies before they had their first dose of vaccine. Anyone with antibodies was excluded.

The average age of the participants was 65, reflecting the older age groups who were the first in the UK to receive Covid vaccines under the NHS’s widely-praised programme that began on 8 December.

Antibody rates initially rise more quickly among those who have had the Pfizer/BioNTech vaccine than those with the Oxford/AstraZeneca one. However, after four weeks the recipients of either demonstrate almost identical antibody positivity rates.

After one dose the vaccines stimulated the production of fewer antibodies in older people, who have been most likely to get severe Covid and die during the pandemic, than younger ones, the UCL Virus Watch project team found. But once everyone had had their second dose people of all ages enjoyed uniformly very high antibody levels.

Antibody levels after one jab are also lower in people with some underlying health conditions, including cancer, diabetes and heart disease, and also those taking immune system suppressing medication, usually for cancer. However, again that difference disappeared once all participants had their second vaccine, the researchers said.

“The UCL Virus Watch data shows that for older adults and for people with underlying health conditions, the antibody response is a bit weaker after the first dose of the vaccine, but strong after the second dose,” said Prof Rob Aldridge, the chief investigator of the UCL Virus Watch study.

“It is a timely reminder about the importance of getting the second dose of the vaccine. But it is also reassuring – vaccines are our way out of the pandemic.”

The co-authors of the paper, which is undergoing peer review before publication in a medical journal, say their findings show that everyone should have both doses of their vaccine so they can be considered “safe”, especially older adults and people with existing ailments.

More than 20 million Britons have now had two doses of either one of those vaccines, or the Moderna vaccine, which started being used in early April.

The researchers include Prof Andrew Hayward, a member of the government’s New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), which has advised ministers during the pandemic. The study was funded by the NHS’s research arm, the National Institute for Health Research (NIHR), and the government’s UK Research and Innovation agency.

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