This report presents an analysis of COVID-19 vaccine effectiveness (VE) after a fourth dose in relation to SARS-CoV-2 infection and severe outcomes due to the omicron variant among persons aged 65 years and older in Sweden. The purpose was to evaluate the duration of the protective effect, compared to unvaccinated individuals. In summary, the protection against severe outcomes due to COVID-19 wane slowly at 120 to 150 days after the fourth dose.

To compensate for the expected waning effects after the fourth dose (the second booster), the Public Health Agency of Sweden has recommended an additional fifth dose (the third booster) to all persons aged 65 years and older and people in risk groups.

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