Pfizer Covid vaccine protection against infection drops to 47%, study confirms

Safeway pharmacist Ashley McGee fills a syringe with the Pfizer COVID-19 booster at a booster clinic in San Rafael, California on October 01, 2021.

Justin Sullivan | Getty Images

The effectiveness of Pfizer and BioNTech’s Covid-19 vaccine against infection declines over several months, falling from a high of 88% per month after receiving the series of two vaccinations to 47% six months later, according to one in the peer on Monday published observational study shows -reviewed journal The Lancet.

While the effectiveness of the two-dose mRNA vaccine against infection wears off, its protection from hospitalization related to Covid remains in place and remains, according to the study, conducted by Pfizer.

The results confirm early reports from the Centers for Disease Control and Prevention and Israeli Health Authorities, which found that infection protection waned over several months, even though it was effective in keeping people out of the hospital.

“Protection against infection decreases in the months after a second dose,” said Dr. Sara Tartof, epidemiologist at Kaiser Permanente and lead author of the study. Kaiser Permanente conducted the research with Pfizer.

The published data comes less than two weeks after U.S. health officials approved the distribution of booster shots of the Pfizer BioNTech vaccine to a number of Americans, including the elderly and other adults, who are considered at risk. Only a limited number of recipients who originally received Pfizer’s vaccines are currently eligible to receive booster vaccinations. The new guideline will make the third dosage of Pfizer available to around 60 million people, of whom 20 million were immediately eligible, President Joe Biden said late last month.

A key Food and Drug Administration advisory committee is scheduled to hold a two-day meeting next week to discuss whether health officials should recommend booster injections to those who have received the vaccines from Moderna or Johnson & Johnson.

Booster vaccination has been a controversial topic for scientists – inside and outside of government – especially since many people in the US and other parts of the world have not yet received a single dose of a vaccine.

The results, released Monday evening, were based on more than 3.4 million electronic health records from Southern California’s Kaiser Permanente health system between December 4th and August 8th. During the study period, the proportion of positive cases attributed to the delta variant increased from 0.6% in April to almost 87% by July.

The researchers found that the effectiveness of the Pfizer vaccine against Delta variant infections was 93% one month after the second dose and decreased to 53% four months later. By comparison, effectiveness against other non-delta variants was 97% after one month and decreased to 67% after four months, the study said.

The effectiveness against delta-induced hospital admissions remained high at 93% for the duration of the study, the researchers said.

The decline in efficacy against infection is “most likely due to the wear off, and not the loss of weight, of Delta or other variants that escape vaccination protection,” said Dr. Luis Jodar, Pfizer’s chief vaccine medical officer.

“Our variant-specific analysis clearly shows that the BNT162b2 vaccine is effective against all current variants of concern, including Delta,” he said in a press release published with the study.

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