Pfizer Vaccine Protection Wanes After 6 Months: Study

Damian McNamara

July 28, 2021

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

Pfizer's COVID-19 vaccine continues to show strong protection against serious illness and hospitalization after 6 months, but overall protection against the virus appears to wane after a half a year, according to a new study.

The July 28 preprint report of the study, which has not been peer reviewed, suggests a gradual "declining trend in vaccine efficacy" over 6 months after a two-dose regimen of the Pfizer vaccine. The study included more than 45,000 people worldwide.

The study found that overall effectiveness fell from 96% to 84%.

A third booster dose of the Pfizer vaccine increases neutralizing antibody levels against the Delta variant by more than five times compared to levels after a second dose in people aged 18 to 55 years, new data from Pfizer show.

The immune response to the third dose appears even more robust ― more than 11 times higher than the response to second shot ― among people aged 65 to 85 years.

The company noted this could mean an estimated 100-fold increase in Delta variant protection after a third dose. These new findings are outlined in a Pfizer second quarter 2021 earnings report, which notes that the data are submitted for publication in a medical journal.

The data come from a relatively small number of people studied. There were 11 individuals in the 18- to 55-year-old group and 12 people in the 65- to 85-year-old cohort.

"These preliminary data are very encouraging as Delta continues to spread," Mikael Dolsten, MD, chief scientific officer and president of the worldwide research, development and medical organization at Pfizer, said during prepared remarks on a company earnings call today, CNN reported.

Availability of a third dose of any of the current COVID-19 vaccines would require either amending the US Food and Drug Administration (FDA) emergency use authorization or granting full FDA approval status to the vaccine.

The possibility of a third-dose authorization or approval has not been without controversy. When Pfizer announced intentions to file for FDA authorization of a booster dose on July 8, the Centers for Disease Control and Prevention, the FDA, and the National Institutes of Health were quick to issue a joint statement saying that they would decide when the timing is right for Americans to have a third immunization. The agencies stated, in part, "We are prepared for booster doses if and when the science demonstrates that they are needed."

In addition, the World Health Organization said at a media briefing on July 12 that rich countries should prioritize the sharing of COVID-19 vaccine supplies to other countries in need worldwide before allocating doses for a booster shot of its own residents.

Damian McNamara is a staff journalist based in Miami. He covers a wide range of medical specialties, including infectious diseases, gastroenterology and neurology. Follow Damian on Twitter: @MedReporter.

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