The first batch of the mRNA for the trial has already been manufactured, Pfizer said. Clinical studies with the booster could begin as early as August, depending on regulatory approval. The adapted shot would target the full spike protein of the Delta variant.

The vaccine maker cites concerns about a risk of waning protection against infection six to twelve months after the two initial doses as a reason that a booster would be warranted – especially in view of the rapid global spread of the more contagious Delta variant.

“The Pfizer vaccine is highly active against the Delta variant," chief scientific officer Mikael Dolsten said in an interview with the Reuters news agency. “But after six months, there likely is the risk of reinfection as antibodies, as predicted, wane."

Leaders of most vaccine makers, led by Pfizer’s CEO Albert Bourla, have said from the outset of vaccinations that in view of the virus’s mutations, they were fairly confident that booster shots could be needed at least after a year.  Some epidemiologists and health organizations have accused them of seeking to boost revenue, however.

In response to Pfizer’s announcement of the  booster plans, the FDA and the US Centers for Disease Control (CDC) have cast a critical eye and said they would adopt a “wait and see” attitude, while World Health Organization (WHO) suggested there could be a need to collect additional data. The WHO told Reuters that “the question is under consideration by researchers.”

Multiple countries in Europe and elsewhere have already approached Pfizer and BioNTech about the booster, and Dolsten said they have received a briefing similar to the one US authorities are due to receive in the near future. Some European countries may begin administering the shots before the FDA clears them for the US, he hinted, noting also that the companies believe the booster shots to be especially important for older age groups.

Pfizer’s placebo-controlled efficacy trial of the booster would be conducted with  10,000 participants and would run through the autumn. In order not to take doses away from people who have not yet received two, the drugmakers are eyeing ways to boost production.

Commenting on Israeli data said to show that the Pfizer/BioNTech vaccine was only 64% effective in real term tests in June, though still 93% effective in preventing a hospitalizations and serious illness, Dolsten said the decline in efficacy among those previously vaccinated could be attributed mainly to infections in people who had been vaccinated in January or February.

The New York-based pharma and the Israeli government have a standing agreement on data sharing in exchange for expedited delivery of vaccines. Pfizer has not yet shared the full set of Israeli data but said it plans to do shortly.

"It's a small data set, but I think the trend is accurate, given that Delta is the most contagious variant we have seen,“ Dolsten told Reuters. After six months, he said, Pfizer's US data showed an erosion of the vaccine’s efficacy against the variants circulating in the spring.

Pfizer and BioNTech have said they do not believe that the current version already given to thousands of people will need to be entirely replaced in order to combat the variant.

Author: Dede Williams, Freelance Journalist