The Oxford/AstraZeneca vaccine induced a stronger cellular immune response in elderly adults than the BioNTech/Pfizer shot, potentially providing more protection against severe Covid-19 and new virus variants.
In the first head-to-head comparison of the two vaccines, scientists discovered that both shots elicited an antibody response in the group of over-80s, tested five to six weeks after the first shot. However, participants who received the AstraZeneca jab were more likely to also have a T-cell response.
Vaccines teach the immune system — which includes both antibodies and T-cells — to recognise part of the Sars-Cov-2 virus. The antibody response of different vaccines has already been studied, but so far less data has been gathered on the T-cell response because it is harder to measure.
In the new study by UK Coronavirus Immunology Consortium and the University of Birmingham, T-cell responses were reported in 31 per cent of recipients of the AstraZeneca vaccine and 12 per cent of those who had a Pfizer jab. These rates are likely to rise after a second dose, because a previous study showed that 63 per cent of the over-80s had a T-cell response after two Pfizer vaccines. The study has yet to be peer-reviewed.
Professor Paul Moss, who leads UK CIC, said the cellular responses could help protect against severe disease and may help the body recognise variants of the virus.
“They [T-cells] are somewhat less susceptible to loss of immune recognition against viral variants than antibody response,” he added. “I think people are confident that the variants will only lose 10 to 20 per cent of the cellular response, whereas they can lose a lot more of the antibody response.”
Experts have been concerned that all of the currently approved Covid-19 vaccines could be less effective against 501.V2, the variant that first emerged in South Africa. One study showed that the AstraZeneca shot did not prevent people from developing mild or moderate disease when infected with the strain.
The new pre-print paper adds to the evidence in favour of spacing out vaccine doses, as in the UK where health authorities have instituted a gap of 12 weeks between injections, rather than the three to four-week interval that was tested in trials and adhered to in most other countries. The UK strategy aimed to ensure as many people as possible would receive a first dose, to increase immunity across the population.
The study found that five to six weeks after the first dose of either vaccine the vast majority of the 165 elderly people — who are more likely to struggle to mount an immune response than younger populations — had developed antibodies.
Some 93 per cent of recipients of the Pfizer inoculation and 87 per cent of those who had the AstraZeneca shot showed spike protein-specific antibodies, likely to have been induced by the vaccine. Responses were stronger for people who had recovered from Covid-19.
“There’s increasing evidence that as a health care measure this decision to delay the vaccine has worked in the UK. We’ve got very good clinical protection from the one dose scheduling,” Moss said.