Vaccines have up to 90% efficacy against severe COVID-19 for
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In the largest study to date, the researchers analyzed data from 7 million unvaccinated and vaccinated individuals. The latter received Pfizer-BioNTech, Moderna or Johnson & Johnson doses of the COVID-19 vaccine. Conducting a systematic review and meta-analysis, the investigators examined 18 peer-reviewed studies published from December 2019 to November 2021, prior to emergence of the omicron variant that dominated the most recent pandemic surge in the U.S.

In their analysis, the researchers determined the vaccines provided significant protection against COVID-19, but effectiveness waned over time. The findings revealed that after full vaccination, immunity against COVID-19 infection decreased from 83% after the first month to 22% after five or more months.

The research included data on adults and children, aged 12 and older. The findings showed that recipients of the Moderna vaccine experienced the highest levels of protection. Fully vaccinated individuals are defined as those who received two doses of either the Moderna or Pfizer vaccines, as well as individuals who received one dose of the Johnson & Johnson vaccine. The researchers did not have data beyond six months, and the study did not include data on booster vaccines.