Another Study Finds COVID-19 Vaccine Effectiveness Turns Negative Within Months

A doctor prepares the Pfizer-BioNTech COVID-19 vaccine at a vaccination center in Halifax, England, on July 31, 2021. Ian Forsyth/Getty Images

The effectiveness of the Pfizer and AstraZeneca COVID-19 vaccines turns negative against severe COVID-19 months after administration, according to a new study.

A single dose of the Pfizer vaccine was pegged at minus 121 percent effectiveness on day 84 and minus 85 percent effectiveness on day 98. A second Pfizer dose held up better, but still dipped below 50 percent at day 98, researchers concluded.