Booster doses were also shown to lose effectiveness over time
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.
“The half-life of VE against symptomatic infection was estimated to be 87 days for Omicron compared with 316 days for Delta. Similar waning rates of VE were found for different age segments of the population.”
“These findings suggest that the effectiveness of COVID-19 vaccines against laboratory-confirmed Omicron or Delta infection and symptomatic disease rapidly wanes over time after the primary vaccination cycle and booster dose,” the study said.
“Putting together the bulk of available evidence on the waning of VE over time against COVID-19 variants has crucial implications for future interventions and vaccination programs.”
Effectiveness by Vaccine Brand
Vaccine effectiveness against Omicron infection was 44.4 percent a month after the completion of the primary vaccination cycle. This fell to 20.7 percent at six months and then to 13.4 percent at nine months. Vaccine effectiveness was found to be higher against the Delta variant as compared to the Omicron variant.
“Pooled estimates of VE after any primary vaccination cycle against symptomatic disease after Omicron infection show a marked waning over time,” the study stated.
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