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According to a study published by US health authorities, the effectiveness of the booster dose of vaccines from Pfizer and Moderna declines over time, but remains high once morest hospitalizations four months following injection.
The study was conducted between late August 2021 and January 2022, covering both waves related to the Delta and Omicron variants.
During both periods, the efficacy measured following a third dose was always higher than following two doses.
Efficacy once morest the Omicron variant rose to 91% for those who received their third dose within two months, but fell to 78% for people who received it four months or more ago.
