The effectiveness of the Pfizer and BioNTech vaccine in preventing coronavirus infection fell from 88% to 47% six months after the second dose, according to data published Monday that was evaluated by US health agencies in the decision on the need for booster doses.
The data, published in the medical journal The Lancet, was released earlier in August, before peer review.
The analysis shows that the vaccine’s effectiveness in preventing hospitalization and death remains high, at 90%, for at least six months, even against the highly contagious delta variant of the coronavirus.
The data suggest that the decrease in the prevention of symptomatic cases is due to decreased efficacy rather than infectious variants, the researchers said.
Scientists at Pfizer and health care provider Kaiser Permanente studied the health records of an estimated 3.4 million people who were members of Kaiser Permanente in Southern California between December 2020 — when the vaccine first became available — and August 2021.
“Our variant analysis clearly shows that the vaccine (Pfizer/BioNTech) is effective against all variants, including Delta,” said Louis Godard, senior vice president and medical director of Pfizer’s Vaccine Division.
Vaccine efficacy against the delta variant was 93% after the first month, dropping to 53% after four months. Against other coronavirus variants, efficacy decreased from 97% to 67%.
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