Pfizer COVID-19 vaccine efficacy drops to 84% after 6 months, preprint study suggests

A new study involving the Pfizer-BioNTech COVID-19 vaccine suggests the jab’s efficacy drops to around 84% about six months after the second dose. The study, which has not yet been peer-reviewed and was published on medRxiv, was supported by Pfizer and BioNTech, concluding that despite “a gradually declining trend in vaccine efficacy,” it still was “highly efficacious in preventing COVID-19.” 

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The data noted that vaccine efficacy peaked between 7 days and two months post-second dose at 96.2%. From two months to four months, efficacy fell to 90.1%, and from four months to six months, it further fell to 83.7%. Researchers calculated a decline in vaccine efficacy about an average of about 6% every two months. The study found that the vaccine overall achieved about 91% efficacy from seven days through six months post-second dose in study participants ages 12 and older. 

“Ongoing follow-up is needed to understand the persistence of the vaccine effect over time, the need for booster dosing, and timing of such a dose,” the study authors wrote, later adding that booster trials are currently underway. 

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Pfizer has previously signaled its intention to file for emergency use authorization for a third shot, which initially drew a sharp response from the CDC and FDA. The agencies said in a statement published earlier this month that fully vaccinated Americans “do not need” an extra dose at this time. 

“FDA, CDC and NIH are engaged in a science-based, rigorous process to consider whether or when a booster might be necessary,” the statement said. “This process takes into account laboratory data, clinical trial data, and cohort data – which can include data from specific pharmaceutical companies, but does not rely on those data exclusively. We continue to review any new data as it becomes available and will keep the public informed. We are prepared for booster doses if and when the science demonstrates that they are needed.” 

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However, Dr. Anthony Fauci recently floated the idea that certain immunocompromised patients may consider getting one. In a CDC advisory panel meeting last week, experts recommended immunocompromised patients who are fully vaccinated should keep wearing masks and socially distancing as the agency weighs the need for potential boosters among this population.