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April 01, 2021

Pfizer's COVID-19 vaccine remains highly protective at least six months after second dose

The shot also appears effective against a variant that has spread rapidly in South Africa

Pfizer's COVID-19 shot remains highly effective for at least six months — though vaccine experts say protection likely lasts much longer. 

Updated data from an ongoing clinical trial shows the vaccine has a 91.3% efficacy rating from one week to six months after recipients receive their second doses. No serious safety concerns have been reported. 

The vaccine's effectiveness was consistent across age, gender, race and ethnicity demographics, as well as among participants with a variety of underlying health conditions.

It also appears to be effective against the B.1.351 variant that has spread rapidly in South Africa. Of the 800 participants enrolled in South Africa, only nine contracted the coronavirus — all of them in the placebo group. Six were confirmed to have contracted the B.1.351 variant. 

The trial data also found the vaccine to be highly effective at preventing severe COVID-19 complications. It was 100% effective at preventing severe COVID-19 complications as defined by the U.S. Centers for Disease Control and Prevention and 95.3% effective as defined by the U.S. Food and Drug Administration. 

Pfizer and BioNTech, which helped develop the vaccine, plan to submit a license application to the FDA, CEO Albert Bourla said. 

"The high vaccine efficacy observed through up to six months following a second dose and against the variant prevalent in South Africa provides further confidence in our vaccine's overall effectiveness," Bourla said. 

Dr. Scott Hensley, an immunologist at the University of Pennsylvania, said vaccine is likely to provide protection for years. 

"These mRNA vaccines — it really seems the level of antibodies they elicit are so high, they are persistent. And the combination of having very high levels of antibodies and persistent levels of protection are the recipe for a very long level of protection against these variants," Hensley told CNN"I would not be surprised if this is a vaccine that we only get once." 

Both the Pfizer and Moderna vaccines rely on mRNA, a novel approach that uses genetic material to trigger an immune response. 

There have been 927 confirmed COVID-19 cases in Pfizer's study, which now involves more than 46,000 volunteers. However, only 77 infections have been found in participants who received the vaccine. The remaining 850 cases were among people who received a placebo.

Only one participant who received the vaccine suffered serious COVID-19 complications, compared to 53 who received the placebo.

Previous studies have found Pfizer's vaccine to be effective against variants that have developed in Brazil and the United Kingdom.

"It is an important step to further confirm the strong efficacy and good safety data we have seen so far, especially in a longer-term follow-up," BioNTech CEO Ugur Sahin said. 

"These data also provide the first clinical results that a vaccine can effectively protect against currently circulating variants, a critical factor to reach herd immunity and end this pandemic for the global population."

On Wednesday, Pfizer released the results of a clinical trial that shows the vaccine is safe and effective at protecting adolescents

The two-shot vaccine was granted an emergency use authorization by the FDA in December. It was the first COVID-19 vaccine to become available in the U.S. Vaccines from Moderna and Johnson & Johnson have since been authorized. 

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