A new study indicates that delaying the second “booster” dose of the Pfizer-BioNTech COVID vaccine (to 11-12 weeks rather than 3 weeks) increases protective immune responses over threefold in individuals over 80 years old.
“This study further supports a growing body of evidence that the approach taken in the UK for delaying that second dose has really paid off,” explained epidemiologist Gayatri Amirthalingam.
So far, more than 1.41 billion COVID vaccines have been administered globally. Two doses of the Pfizer, Moderna, and Oxford-AstraZeneca COVID vaccines are required for individuals to build a robust, protective antibody response against SARS-CoV-2. This is the first study demonstrating that delaying the second dose strengthens this immune response, a finding that could inform vaccine scheduling decisions.
Amirthalingam and colleagues tracked antibody responses in 175 vaccinated individuals over the age of 80. The two groups of participants received the booster shot either 3 weeks or 11-12 weeks after the first one. The researchers found that peak antibody levels were around 3.5 times greater in those who waited longer.
While this data is specific to the Pfizer vaccine (one that is currently only available to select countries), follow up studies will need to determine whether similar immune dynamics also apply to delaying the second shot for other vaccines.
For now, maintaining restrictions during the vaccine rollout is important, given that the first dose only provides people with partial immunity to COVID.