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By Manas Mishra
(Reuters) – The effectiveness of the Pfizer Inc / BioNTech SE vaccine in preventing coronavirus infection fell to 47% from 88% six months after the second dose, according to data released Monday that U.S. health agencies were taken into account in deciding the need for booster injections.
The data, which was published in the medical journal published by Lancet, had already been published in August ahead of the peer review.
The analysis showed that the vaccine’s efficacy in preventing hospitalizations and deaths remained high at 90% for at least six months, even against the highly contagious Delta variant of the coronavirus.
The data suggests the drop is due to waning efficacy, rather than more contagious variants, the researchers said.
Researchers at Pfizer and Kaiser Permanente studied electronic health records of approximately 3.4 million Kaiser Permanente Southern California members between December 2020 – when the vaccine first became available – and August 2021 .
“Our variant-specific analysis clearly shows that the vaccine (Pfizer / BioNTech) is effective against all current variants of concern, including Delta,” said Luis Jodar, senior vice president and medical director of Pfizer Vaccines.
A potential limitation of the study was a lack of data on adherence to masking guidelines and occupations in the study population, which could have affected the frequency of testing and the likelihood of exposure to the virus.
The efficacy of the Delta variant vaccine was 93% after the first month, decreasing to 53% after four months. Against other coronavirus variants, the effectiveness decreased to 67% from 97%.
“To us, this suggests that Delta is not an escape variant that escapes vaccine protection altogether,” said study leader Sara Tartof of the Kaiser Permanente Southern California Research and Evaluation Department.
“If that was the case, we probably wouldn’t have seen high protection after vaccination, because vaccination would not work in this case. It would start weak and stay low.”
Variant testing is more likely to fail in vaccinated individuals, which could lead to an overestimation of the variant-specific efficacy in the study, the authors cautioned.
The United States Food and Drug Administration has authorized the use of a booster dose of the Pfizer / BioNTech vaccine for the elderly and some Americans at high risk of infection. Scientists asked for more data on whether boosters should be recommended for everyone.
(Reporting by Manas Mishra in Bengaluru; Editing by Bill Berkrot)
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