April 1 (UPI) -- Pfizer and partner BioNTech announced Thursday that six months after getting the second dose of its vaccine, volunteers in a clinical trial remained 91% protected against COVID-19 and were better protected against severe forms of the illness.
The 12,000 volunteers showed no serious safety concerns, but many did have usual short-term side effects such as a sore arm or fatigue.
The findings come from a new study of a 46,000-person clinical trial. The vaccine has already been administered to nearly 80 million Americans.
Out of more than 900 trial participants who fell ill with COVID-19 more than a week after their second dose, only 77 had received the active vaccine. That result is compared with 850 who received a placebo.
Pfizer said the vaccine has proved to be 95% effective in preventing severe COVID-19, and was 100% effective in preventing cases among 800 volunteers in South Africa, where the B.1.351 coronavirus variant was prevalent.
The companies are expected to apply to the Food and Drug Administration soon to fully license the vaccine. All three available COVID-19 vaccines in the United States, from Pfizer-BioNTech, Moderna and Johnson & Johnson, are being distributed under emergency use authorization rather than full FDA licenses.
The FDA allowed the companies to present only two months of data for emergency use. The usual process typically requires data from at least six months.
"These data confirm the favorable efficacy and safety profile of our vaccine and position us to submit a Biologics License Application to the U.S. FDA," Pfizer CEO Albert Bourla said in a statement.
The agency has said it would consider issuing a full license once the companies meet the typical requirement for vaccines that prevent other infectious diseases.
Wednesday, Pfizer announced that the vaccine has shown in clinical testing to be highly effective and well tolerated in children between the ages 12 and 15.