Pfizer plans to ask US regulators to authorise a booster dose of its COVID-19 vaccine within the next month, the drugmaker's top scientist says, based on evidence of greater risk of reinfection six months after inoculation and the spread of the highly contagious Delta variant.
The US Food and Drug Administration (FDA) and the Centers for Disease Control and Prevention (CDC) said, however, in a joint statement that Americans who had been fully vaccinated do not need a booster COVID-19 shot at this time.
Some scientists have also questioned the need for booster shots.
Pfizer's chief scientific officer, Mikael Dolsten, said the recently reported dip in the vaccine's effectiveness in Israel was mostly due to infections in people who had been vaccinated in January or February. The country's health ministry said vaccine effectiveness in preventing both infection and symptomatic disease fell to 64 per cent in June.
"The Pfizer vaccine is highly active against the Delta variant," Dolsten said in an interview. But after six months, he said, "there likely is the risk of reinfection as antibodies, as predicted, wane".
Pfizer did not release the full set of Israeli data on Thursday, but said it would be published soon.
"It's a small data set, but I think the trend is accurate: six months out, given that Delta is the most contagious variant we have seen, it can cause infections and mild disease," Dolsten said.
The FDA and CDC, in their joint statement, said: "We are prepared for booster doses if and when the science demonstrates that they are needed."
Pfizer's own data from the United States showed an erosion of the vaccine's efficacy to the mid-80s after six months, Dolsten said, against the variants circulating there in the spring.
He stressed that data from Israel and Britain suggested that even with waning antibody levels, the vaccine remained about 95 per cent effective against severe disease.
The vaccine, developed with German partner BioNTech SE , showed 95 per cent efficacy in preventing symptomatic COVID-19 in a clinical trial the companies ran last year.
Dolsten said early data from the company's own studies showed that a third booster dose generated antibody levels that were five to 10 times higher than after the second dose, suggesting a third dose will offer promising protection.
He said multiple countries in Europe and elsewhere had already approached Pfizer to discuss booster doses, and some may begin administering them before a potential US authorisation.
Dolsten said he believes booster shots are particularly important in older age groups.