The effectiveness of COVID-19 vaccines fell below 20 percent a few months after vaccination, with booster shots seeing effectiveness drop below 30 percent.
The review, published in the JAMA Network journal on May 3, analyzed 40 studies estimating vaccine effectiveness (VE) over time against laboratory-confirmed COVID-19 infection and symptomatic disease. The studies were selected from 799 original articles, 149 reviews published in peer-reviewed journals, and 35 preprints. The review found that the vaccine effectiveness of a primary vaccination cycle against the Omicron infection and symptomatic disease was lower than 20 percent at 6 months from the administration of the last dose.
Booster doses restored vaccine effectiveness to levels similar to those seen after administration of the primacy cycle dose. However, nine months after the booster dose, vaccine effectiveness against Omicron was found to be lower than 30 percent against infection and symptomatic disease….