Delaying second Pfizer COVID-19 shot boosts immune response in over-80s, study finds

Delaying the second dose of the Pfizer–BioNTech COVID-19 vaccine by 12 weeks after the first dose significantly boosts antibody responses in elderly people, according to a new U.K. study.

Researchers from the University of Birmingham and Public Health England (PHE) found that peak antibody levels were 3.5 times higher in those who waited 12 weeks for their booster shot, compared with those who had it after a three-week gap.

The study, which was published as a preprint and hasn’t yet been peer-reviewed, will lend support to the U.K. government’s decision at the start of its COVID-19 vaccine rollout in December 2020 to delay second doses of the vaccines to inoculate the elderly and vulnerable quicker, and ease the tight supplies.

At the time, the strategy divided experts, as drug regulators had authorized use of both the shot developed by drug company Pfizer PFE, +0.31% and its partner BioNTech BNTX, +0.33% and the shot produced by drug company AstraZeneca AZN, +0.45% AZN, +0.95% with the University of Oxford on the basis of clinical trials that had spaced out the doses by only three or four weeks.

“This study further supports a growing body of evidence that the approach taken in the U.K. for delaying that second dose has really paid off,” said Dr. Gayatri Amirthalingam, a PHE epidemiologist and a co-author of the study, to reporters at a briefing.

Researchers said the study of 175 people aged 80 and over is the first direct comparison of how such a delay affects the immune response in any age group for the different intervals. An earlier study from the University of Oxford found that a single dose of the AstraZeneca–Oxford vaccine provides a high level of protection when boosters of the shot were delayed for 12 weeks.

The Birmingham researchers also looked at another part of the body’s immune response, found in T cells, which destroy any cells that have been infected with the virus. The peak T cell responses were higher in the group with a three-week interval between doses, the researchers found, but they cautioned that it wasn’t yet clear how protected individuals were based on which dosing schedule they received. “Research is required to further explore these variations in responses, the authors noted.

Separately on Friday, PHE said that COVID-19 vaccinations in the U.K, had directly prevented an estimated 11,700 deaths of people aged 60 and over by the end of April, and kept 33,000 people aged 65 and older out of hospital.

“As these figures highlight, getting your vaccine could save your life or stop you becoming seriously ill from COVID-19. It will also significantly reduce your chances of getting infected and infecting others,” said Dr. Mary Ramsay, PHE’s head of immunization.

“It is vital to get both doses of your vaccine when you are offered it,” she added.