Pfizer Inc. will seek clearance from U.S. regulators in coming weeks to distribute a booster shot of its Covid-19 vaccine to heighten protection against infections, as new virus strains rise.
The company also said it plans to start clinical trials in August of an updated version of its vaccine that would better protect against the Delta variant.
Pfizer and partner BioNTech SE said Thursday that they will seek authorization for the third shot, based on encouraging initial study data.
The companies said the data showed that a booster shot given at least six months after the second dose produced antibodies protective against the original strain of the virus and a more recent strain, Beta.
The companies said the antibody levels were five to 10 times higher than after two doses.
The companies said they expect their booster shot to provide similarly higher levels of protection against the Delta variant.
In addition, Pfizer and BioNTech said they have begun producing the updated vaccine for testing in people.
While we believe a third dose of BNT162b2 has the potential to preserve the highest levels [of] protective efficacy against all currently known variants including Delta, we are remaining vigilant,” the companies said, using the code name for their original vaccine.
The moves are the strongest sign to date of vaccine makers efforts to confront new variants of the virus better able to elude existing shots.
To date, companies have been evaluating the effectiveness of their shots against new variants and working on boosters and new vaccines targeting the strains.
Pfizer and BioNTech are the first to say they will ask regulators to authorize a booster that could increase their vaccines protection against the strains.
It isnt clear, however, whether vaccine experts would recommend that most people receive a third booster shot if one was authorized by the FDA.
Federal health officials signaled they would take a cautious view toward authorizing booster shots, which they said arent currently necessary.
Americans who have been fully vaccinated do not need a booster shot at this time,” the Food and Drug Administration and Centers for Disease Control and Prevention said in a joint statement issued Thursday evening. FDA, CDC, and NIH are engaged in a science-based, rigorous process to consider whether or when a booster might be necessary.”
The agencies said they might look at data from pharmaceutical companies but wouldnt rely on that data exclusively. They also said Covid-19 vaccines provide strong protection against the Delta variant.
People who are fully vaccinated are protected from severe disease and death, including from the variants currently circulating in the country such as Delta,” the agencies said. Virtually all Covid-19 hospitalizations and deaths are among those who are unvaccinated.”
Monica Gandhi, a professor of medicine and infectious disease specialist at the University of California, San Francisco, said that booster shots arent necessary except for those who have compromised immune systems and the very elderly.
Recent peer-reviewed studies, she said, have shown that two shots of the Pfizer vaccine are adequate to protect against variants including Delta.
I am very concerned that there is a profit motive for this announcement, rather than sound scientific reasoning,” Dr. Gandhi said. I would encourage Pfizer to work on producing more mRNA vaccines for the world to help diminish the chance of future variants.”
Antibody levels would be expected to go down several months after vaccination as the immune system revs down, said Ronny Gal, a Sanford C. Bernstein pharmaceuticals analyst. Yet the immune system retains the ability to remobilize protective antibodies if they are exposed to the virus again in the future, helping prevent severe illness even if there is infection, he said.
For now, Mr. Gal said he doesnt expect widespread use of booster shots if they are authorized unless new evidence emerges that two shots stop protecting against illness.
The Pfizer-BioNTech vaccine was the first to be authorized in the U.S., and has been cleared for use in people 12 years and older.
Studies have indicated that the shot protects well against new variants of the virus that have emerged since the companies began developing their original version, especially after the second dose.
The vaccine doesnt offer as much protection after the first of two doses, however. And the companies said that it appears that the vaccines effectiveness begins to wane about six months after the second dose, based on their own clinical trials and recent data released by the Israeli Ministry of Health.
Israel said earlier this week that the shot protected 64% of inoculated people from infection during an outbreak of the Delta variant, down from 94% before.
The vaccine still provided 94% protection against severe illness during the outbreak, compared with 97% before, the health ministry said.
The Delta variant was first identified in India, where cases caused by the strain overwhelmed the countrys hospitals.
Since then, it has spread rapidly around the globe, including in the U.S.
This week, federal health officials said it was now the most common strain in the U.S.
The variant appears to be more contagious than earlier versions of the virus and better able to evade vaccines.
Health authorities have encouraged people to be vaccinated to better ward off the Delta variant, saying more than 99% of Covid-19 deaths in the U.S. are among the unvaccinated.
Write to Joseph Walker at joseph.walker@wsj.com
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