Pfizer Says Third Shot of Vaccine Boosts COVID-19 Protection

New data show that protection from both doses of the Pfizer COVID-19 vaccine decreases slightly over time but that a third dose significantly boosts levels of antibodies against several variants of the virus, including the highly contagious delta variant that is now dominant in the United States.

The study of 42,000 volunteers in six countries found that the vaccine had an efficacy rate of about 96 percent against symptomatic COVID-19 for the first two months following the second dose, but that declined by about 6 percent every two months after that, reaching 83.7 percent after six months, The New York Times reported. The vaccine's efficacy against severe disease held steady at about 97 percent, according to the findings posted online July 28 on the preprint server medRxiv. The study ended before the rise of the delta variant.

In addition, Pfizer disclosed that a third dose of its vaccine significantly increases blood levels of antibodies against the delta variant and other variants of the virus. Those preliminary findings were included in an earnings statement and have not been peer-reviewed or published in a scientific journal. More conclusive results are expected in the coming weeks.

Pfizer has said it plans to seek U.S. approval for a third booster shot of its vaccine, but the issue has been controversial. U.S. federal health officials have said boosters for the general population are unnecessary, and experts question whether vaccinated people should get booster shots when so many people in the United States and worldwide have yet to receive a first shot, according to The Times.