Despite the 95% effectiveness in preventing coronavirus infection after two doses of its vaccine, Pfizer is now seeing what a third dose can do.
The company announced on Thursday that a booster dose is being studied among people who received the first doses of the vaccine more than six months ago.
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In an interview with NBC News, Lester Holt, Pfizer’s CEO Albert Bourla said that the hope is that a third dose will further increase the immune response, offering better protection against variants.
“We believe that the third dose,” said Bourla, “will increase the antibody response 10 to 20 times.”
The new study will monitor the safety and efficacy of a third dose in two age groups: 18 to 55 and 65 to 85. Participants come from a group of people who were among the first to receive the Pfizer-BioNTech vaccine: people who volunteered for Pfizer’s initial Phase 1/2 clinical trial, which started in May.
During that trial, participants received two doses of the vaccine three weeks apart. The same dose range is what is currently recommended.
The third photo will be exactly the same as the participants took a year ago.
Pfizer also plans to start testing whether a modified version of the vaccine works well against the South African variant.
In fact, as SARS-CoV-2 changes, vaccines may need to be adjusted. The Food and Drug Administration issued guidance on Monday, saying vaccine manufacturers may be able to avoid lengthy clinical trials to prove the safety and efficacy of vaccines that have been adjusted to account for variants.
This is not much different from how the flu vaccine changes from year to year, responsible for the strains most likely to infect people.
“Every year, you need to get the flu shot,” said Bourla. “It will be the same with Covid. In a year, you will have to go and get your annual chance to protect Covid.”
This suggests that, even when the pandemic is over, Covid-19 may be here to stay. Ongoing studies of redesigned vaccines are needed to understand when reinforcements may be needed, external experts said.
“You need to launch a wide network to find Goldilocks,” said John Grabenstein, former executive director of medical affairs for vaccines at Merck and a former Department of Defense immunologist. “You want to look at shorter intervals, you want to look at longer intervals, to determine when is the best time, if necessary, to revaccate.”
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To date, evidence suggests that the existing Pfizer-BioNTech vaccine remains effective against variants first identified in the UK, Brazil and South Africa.
Bourla said the company’s goal, if and when another variant appears, is to rotate and adjust the current vaccine within 100 days.
Moderna, which makes a vaccine similar to Covid-19, announced on Wednesday that it also began to study the effects of adding a third dose to its regimen and developed a version of the vaccine for the South African variant.
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