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Pfizer’s vaccine protection against COVID-19 wanes slightly

felix gussone

Reviewed by Felix Gussone, MD, written by Health Guide Team

Last updated: Jul 30, 2021
1 min read


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

The new research released by Pfizer and its partner BioNTech looked at data gathered from 44,000 people who participated in Pfizer’s Phase 3 clinical trial last year. The researchers found that the vaccine was overall 97 percent effective at preventing severe disease (low blood oxygen levels or hospitalization) from COVID-19 for at least six months. However, the vaccine’s efficacy in preventing any COVID-19 infection (even with minor symptoms) fell from 96 percent in the first two months after vaccination to 84 percent after six months.

The findings aren’t bad news. Experts have expected that the vaccine’s protection was going to wane a little bit, but they weren’t sure if the protection was going to decrease to a degree that it negatively affects hospitalizations and deaths. So far, that doesn’t appear to be the case. The main goal is to keep people out of the hospital and prevent them from dying, and the vaccines seem to do that. 

One important caveat is that the study hasn’t yet been peer-reviewed or published in a medical journal.  


  1. Stephen J. Thomas, Edson D. Moreira Jr. (2021). Six Month Safety and Efficacy of the BNT162b2 mRNA COVID-19 Vaccine. C4591001 Clinical Trial Group. medRxiv 2021.07.28.21261159; do: 10.1101/2021.07.28.21261159. Retrieved from: