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Despite being 95% effective in preventing coronavirus infection after two doses of its vaccine, Pfizer is now seeing what a third dose could do.
The company announced Thursday that a booster dose is being studied in people who received their first doses of the vaccine more than six months ago.
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In an interview with NBC News’ Lester Holt, Pfizer CEO Albert Bourla said the hope was that a third dose will boost the immune response even more, providing better protection against the variants.
“We believe the third dose,” said Bourla, “will increase the antibody response 10 to 20 fold.”
The new study will monitor the safety and effectiveness of a third dose in two age groups: 18 to 55 years old and 65 to 85 years old. The participants came 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 began in may.
In this trial, participants received two doses of the vaccine three weeks apart. The same dose interval is what is currently recommended.
The third shot will be exactly the same as the participants’ one a year ago.
Pfizer also plans to start testing whether a modified version of the vaccine works well against the South African variant.
This is because as SARS-CoV-2 changes, vaccines may need to be changed. The Food and Drug Administration on Monday released guidelines indicating that vaccine makers may be able to move away from lengthy clinical trials to prove the safety and effectiveness of vaccines that have been modified to accommodate variants.
It’s not unlike how the flu shot changes from year to year, considering which strains are most likely to infect people.
“Every year you have to go get your flu shot,” Bourla said. “It’s going to be the same with Covid. In a year, you will have to go get your annual vaccine so that Covid is protected.
This suggests that even when the pandemic ends, Covid-19 could be here to stay. Ongoing studies of the redesigned vaccines are needed to understand when boosters may be needed, outside experts said.
“You have to cast a wide net to find Goldilocks,” said John Grabenstein, former executive director of medical affairs for vaccines at Merck and former Defense Department immunologist. “You want to watch at shorter intervals, you want to watch at longer intervals, to determine when is the best time, if necessary, to revaccinate.”
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So far, 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 emerges is to pivot and adjust the current vaccine within 100 days.
Moderna, which makes a similar vaccine against Covid-19, said on Wednesday that it has also started studying the effects of adding a third dose to its regimen and has developed a version of the vaccine designed to target the African variant of South.
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