Early data seem to suggest that mRNA vaccine boosters are more effective than additional doses of the adenovirus-vector COVID-19 vaccines from AstraZeneca and Johnson & Johnson.
But scientists don’t currently have “any real clinical effectiveness data on this question,” said Dr. Janet Woodcock, acting FDA commissioner.
To date, vaccine developers have heavily relied on antibody response data to measure the immune response additional vaccine doses offer.
“We really don’t know the connection between [antibody response data] and actually how well protected somebody is,” Woodcock said.
Further complicating matters is the fact that such antibody levels are a measure of a short-term immune response, said Dr. Peter Marks, director of the Center for Biologics Evaluation and Research (CBER) at FDA.
“That’s not to discourage people from getting these boosters,” Marks said.
But scientists have comparatively little data on T cell immunity to COVID-19, which is involved in longer-term immunity. “And it is indeed possible that something that does not give you as high of a level of the antibodies upfront may protect you for a longer period of time, or more robustly later on,” Marks said.
Because of the lack of data, FDA has decided that a non-committal approach would work best about recommending combinations of boosters. Any combination of boosters may be reasonable for most people.
Individuals who had a bad reaction to prior COVID-19 vaccination, however, should research with their physician the prospect of receiving a different type of booster, Woodcock said.
In the future, it is possible that authorities treat COVID-19 boosters as largely interchangeable, Marks hinted. “Most people don’t know what brand flu vaccine they received and although they’re somewhat more standardized [than COVID-19 vaccines],” Marks said.
A flexible strategy for providing COVID-19 boosters could facilitate vaccination — especially in “institutions where it might be hard to go patient by patient and figure out what they received six or eight months ago,” Marks said.
Filed Under: Infectious Disease