Pfizer COVID-19 vaccine 90% effective at preventing hospitalization, even with delta variant: Study

The Pfizer COVID-19 vaccine remains 90% effective at reducing a person's risk of hospitalization from the virus six months after it is administered, a new study has found. This is true even in the face of the delta variant as well as if the person has not received a booster shot.

Still, when it comes to preventing infections, the vaccine's effectiveness wanes rapidly as time passes, the study found. After five months, it is just 47% effective at preventing infection.

In the study, funded by Pfizer, researchers assessed data from Kaiser Permanente and calculated the percentages of fully vaccinated patients who contracted COVID-19 on a monthly basis after vaccination. Data from roughly 3.4 million people was analyzed between December 2020 and August 2021.

The results of the study are in line with previously published data from Israel and the U.S. Centers for Disease Control and Prevention that looked at vaccine effectiveness over time, but the Pfizer-funded study is the first to consider how the delta variant may impact Pfizer vaccine effectiveness over time.