A small study of elderly people finds that delaying a second dose of the Pfizer coronavirus vaccine for three months produces an even stronger antibody response than giving it on the recommended schedule of three weeks after the first dose.
But it’s not clear whether that translates into stronger protection in real life – and the delayed vaccination schedule resulted in lower levels of immune system cells that are involved in long-term protection from disease, the researchers in Britain reported.
The findings are published on a pre-print online server called medRxiv and have not been peer-reviewed.
Dr. Helen Parry of the University of Birmingham and colleagues studied 172 volunteers 80 and older who got Pfizer/BioNTech’s coronavirus vaccine either as the company recommends – two doses given three weeks apart – or on a delayed schedule of two doses given 12 weeks apart. Britain initiated the delayed vaccine schedule to try to stretch a limited vaccine supply and get more first doses to more people.
Some researchers have argued that delaying the second dose of vaccine can be expected to produce a stronger immune response than a shorter interval.
“We demonstrate that both approaches generate high levels of antibody response but peak values are 3.5-fold higher with the extended-interval protocol,” Parry’s team wrote.
But the shorter, three-week interval produced stronger cellular responses, they said. It’s not clear what that means for long-term immunity, they added.
“Our findings confirm previous studies showing that the three-week standard-interval BNT162b2 regimen elicits strong antibody responses in older people,” they concluded. “It will be important to assess how antibody levels are maintained over longer periods and this is likely to define the potential need for booster vaccines in this vulnerable age group.”
The researchers have not studied whether people who get a delayed second dose are more or less likely in real life to become infected with coronavirus.
“The data in this preprint, from a sizeable study of older people, suggest that delaying the second dose of the Pfizer/BioNtech COVID-19 vaccine from three weeks to 12 weeks has the advantage of substantially enhancing the antibody response at the cost of slightly reducing the cellular immune response,” immunologist Eleanor Riley of the University of Edinburgh, who was not involved in the research, said in a statement.
“Nevertheless, both regimens induce significant antibody and cellular immune responses and, when taken together with the emerging clinical efficacy data, suggest that there is no detriment in delaying the second dose of the vaccine.”