"Many variants are coming, and Omicron was the first one that was able to evade -- in a skillful way -- the immune protection that we're giving," Bourla told CBS' "Face the Nation."
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"The protection we are getting from the third (dose) it is good enough -- actually quite good for hospitalizations and deaths," Bourla said.
But protection after three doses is "not that good against infections" and "doesn't last very long" when faced with a variant like Omicron.
"It is necessary, a fourth (dose) for right now," Bourla told CBS.
Currently, anyone ages 12 and up who got a second dose of the Pfizer vaccine at least five months ago can get a third dose.
Anyone ages 18 and up who got the two-dose Moderna vaccine should get a booster shot six months after the second dose, according to the US Centers for Disease Control and Prevention.
And anyone who got the single-dose Johnson & Johnson vaccine should get a booster shot after two months, the CDC said.
Some moderately or severely immunocompromised people who have had three doses of the Pfizer/BioNTech or Moderna Covid-19 vaccines can already get a fourth dose of vaccine, according to the CDC.
But it's not clear if or when the US Food and Drug Administration might authorize a fourth dose of Covid-19 vaccine for healthy teens and adults.
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"We are just submitting those data to the FDA, and then we'll see what the experts also would say outside Pfizer," Bourla told CBS.
Kids under 5 might soon be able to get vaccinated
Currently, children ages 5 to 11 are eligible for two pediatric doses of Pfizer's Covid-19 vaccine but are not yet eligible for a booster. Pfizer is testing a third dose in that age group now.
And kids under age 5 are not yet eligible for a Covid-19 vaccine -- though that could change this spring, Bourla said.
Initial trial data in children ages 2 to 5 showed two doses of a smaller, child-sized vaccine didn't give the expected immunity in the 2- to 5-year-olds -- though it did for babies ages 6 months to 2 years.
So Pfizer decided to add a third child-sized dose for children under age 5 in its ongoing trial.
Pfizer should have data on its three-dose vaccine trial for children ages 6 months to 5 years by April, Bourla told CBS on Sunday.
If authorized by the FDA and recommended by the CDC, Covid-19 vaccines for children ages 6 months to 5 years might start as early as May, Bourla said.
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A shot at a longer-lasting vaccine against all variants
Pfizer and Moderna have said they are working on a vaccine that would specifically protect against the Omicron variant. It's not clear yet if one is needed.
Bourla said Pfizer is also hoping to make a vaccine that will protect against Omicron and all other variants of SARS-CoV-2 -- the virus that causes Covid-19.
The goal is to create "something that can protect for at least a year," Bourla told CBS on Sunday.
"And if we are able to achieve that, then I think it is very easy to follow and remember so that we can go back to really the way (we) used to live," he said.
The-CNN-Wire
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