Amid persistent concerns that the protection offered by COVID-19 vaccines may be waning, a report released [September 17] by the Centers for Disease Control and Prevention finds that America’s workhorse shot is significantly less effective at preventing severe cases of disease over the long term than many experts had realized.
Data collected from 18 states between March and August suggest the Pfizer-BioNTech vaccine reduces the risk of being hospitalized with COVID-19 by 91% in the first four months after receiving the second dose. Beyond 120 days, however, that vaccine efficacy drops to 77%.
Meanwhile, Moderna’s vaccine was 93% effective at reducing the short-term risk of COVID-19 hospitalization and remained 92% effective after 120 days.
Both the Pfizer and Moderna vaccines are based on mRNA technology, which delivers temporary instructions to the body’s muscle cells that help it learn to recognize the spike protein, a key part of the coronavirus’ structure. But “they’re actually not necessarily interchangeable,” said Dr. Timothy Brewer, a professor of medicine and epidemiology at UCLA.
Each vaccine is formulated and administered differently, Brewer said, and those differences could affect the strength and duration of the two vaccines’ protection.
