Among the more than 44,000 clinical trial members, 927 were diagnosed with COVID-19.
Albert Bourla provided an update as to how those who receive his company's vaccine will need to be treated in the coming years. "It is extremely important to suppress the pool of people that can be susceptible to the virus", Bourla said.
Pfizer published a study earlier this month that said its jab is more than 91 percent effective at protecting against the coronavirus, and more than 95 percent effective against severe cases of Covid-19 up to six months after the second dose. "And again, the variants will play a key role", he told CNBC's Bertha Coombs during an event with CVS Health.
Pfizer was first to market in the US with its BioNTech-partnered COVID-19 vaccine, and by and large, it's avoided the safety and supply concerns plaguing some of its pandemic peers.
While time will tell if additional doses are needed and how regularly, such boosters might not be needed as often as the annual flu shot, said Joseph Eisenberg, a University of MI expert in global diseases.
"It is likely that the countries that have already achieved high vaccine coverage are going to be ready to shift their focus to boosters in 2022 and possibly even starting at the end of this year", Corinne M. Le Goff, PharmD, Moderna's chief commercial officer, said during a call with investors, Business Insider reported.
And Bourla said Thursday the company was working on a new formula that would allow the vaccine to be stored for four to six months at a normal temperature, rather than the minus 70 degrees Celsius (minus 94 Fahrenheit) or below now required.
Among the most vulnerable population - residents 65 years and older - more than 70% have gotten a first dose, and more than 61% are fully vaccinated.
He suggested that there would likely be a situation where people will need to get yearly vaccines to remain protected from the worst effects of COVID-19.
"We don't know everything at this moment", he told the House Select Subcommittee on the Coronavirus Crisis. "It seems strong but there is some waning of that and no doubt the variants challenge. they make these vaccines work harder". And after receiving a third shot, people should expect re-vaccination every year, he said. Research has shown that people who get vaccinated have more antibodies than those who were naturally infected.