The effectiveness of the Pfizer-BioNTech COVID-19 vaccine waned over six months, but experts say the data still don't point to an immediate need for booster shots.
The study, which hasn't yet been peer-reviewed or published in a medical journal, found that the vaccine was 97 percent effective at preventing severe disease from COVID-19 for at least six months — but the effectiveness against any symptomatic illness dropped from 96 percent to 84 percent in the same period, falling by about 6 percent every two months.
"I was generally encouraged by the results of the paper," said the lead study author, Dr. Stephen Thomas, a coordinating investigator for the Pfizer vaccine trial and director of the SUNY Upstate Institute for Global Health & Translational Science in New York.
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He said the expectation was always that the vaccine's protection was going to wane. The big question, he said, was whether it would wane to a degree that would affect the so-called public health burden of the disease, specifically hospitalizations and deaths. So far, that doesn't appear to be the case.
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