LONDON - People in England who have received 2 doses of Pfizer's COVID-19 vaccine are generating strong antibody responses as the shot is rolled out, researchers said Thursday, adding that confidence in vaccines was high.

An Imperial College London survey showed 87.9 percent of people over the age of 80 tested positive for antibodies after 2 doses of the Pfizer-BioNTech vaccine, rising to 95.5 percent for those under the age of 60 and 100 percent in those aged under 30.

"Although there is some fall-off in positivity with age, at all ages, we get that very good response to 2 doses of the vaccine," Paul Elliott, Chair in Epidemiology and Public Health Medicine, Imperial College London, told reporters.

Antibody levels are only one part of the immunity picture, with vaccines also shown to generate strong T-cell protection.

Nearly 95 percent of under-30s tested positive for antibodies 21 days after 1 dose, but this fell in older groups.

The research found 34.7 percent of those 80 years or older generated antibody responses from 1 dose of the Pfizer vaccine, but Britain's Joint Committee on Vaccination and Immunization (JCVI) has previously found high protection from the Pfizer vaccine after 1 dose, even when antibody levels are lower.

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Britain has extended the gap between doses to 12 weeks, even though Pfizer has cautioned it only has data for clinical efficacy with a 3-week gap between shots.

Over 154,000 participants took part in Imperial's home surveillance study for COVID-19 antibodies, which monitors antibody levels from natural infection as well as among the vaccinated, between Jan. 26 and Feb. 8.

The survey also looked at confidence in vaccines, and showed it was high, with 92 percent having accepted or were planning to accept a vaccine offer, though confidence was lower among Black people, dropping to 72.5 percent.

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