February 8, 2022

Vaccine effectiveness against COVID-19 during 9 months after second vaccination

Editor's Note

This study by researchers at Umea University in Sweden finds a progressive waning in vaccine effectiveness against COVID-19 of any severity during the first 9 months after the second vaccination, with the rate of waning differing by vaccine type

Analyzing the total population of Sweden, vaccine effectiveness was more than 90% in the first month, with waning starting soon thereafter and ultimately resulting in a non-detectable vaccine effectiveness after 7 months.

Vaccine effectiveness with respect to the risk of hospitalization or death seemed to be better maintained than effectiveness against infection, though there was some waning after 4 months.

Also, overall evidence suggests lower vaccine effectiveness in men than in women and in older people than in younger people.

The results have important clinical implications, as they strengthen the rationale for administration of a third vaccine dose as a booster, especially to high-risk populations, the authors say.


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