LONDON (Reuters) – People in England who received two doses of the Pfizer COVID-19 vaccine are generating strong antibody responses as the injection is given, the researchers said on Thursday, adding that confidence in the vaccines was high.
A survey by Imperial College London showed that 87.9% of people over 80 tested positive for antibodies after two doses of the Pfizer-BioNTech vaccine, increasing to 95.5% for those under 60 and 100% for those under 30 years old.
“Although there is some drop in positivity with age, at all ages, we get a very good response to two doses of the vaccine,” Paul Elliott, president of Epidemiology and Public Health Medicine at Imperial College London, told reporters.
Antibody levels are only part of the immunity picture, with vaccines also showing strong T-cell protection.
Nearly 95% of those under 30 tested positive for antibodies 21 days after a dose, but this declined in the older groups.
The survey found that 34.7% of those 80 years or older generated antibody responses from a dose of the Pfizer vaccine, but Britain’s Joint Vaccination and Immunization Committee (JCVI) had already found high protection from the Pfizer vaccine after a dose, even when antibody levels are lower.
Britain has extended the dose interval to 12 weeks, although Pfizer has warned that it only has clinical efficacy data with a three-week interval between vaccines.
More than 154,000 participants participated in Imperial’s home surveillance study for COVID-19 antibodies, which monitors the levels of antibodies to natural infections, as well as among those vaccinated, between 26 January and 8 February.
The survey also looked at confidence in vaccines and showed that it was high, with 92% having accepted or planning to accept a vaccine offer, although confidence was lower among blacks, dropping to 72.5%.
(Reporting by Alistair Smout; Editing by Giles Elgood)