COVID-19 vaccine effectiveness against severe disease from the Omicron BA.1 and BA.2 subvariants: surveillance results from southern Sweden, December 2021 to March 2022
We compared vaccine effectiveness (VE) against severe COVID-19 during calendar periods from December 2021 to March 2022 when Omicron BA.1 and BA.2, respectively, were the dominating virus variants in Scania county, Sweden. We used continuous density case-control sampling matched for sex and age, and with further adjustment for differences in comorbidities and prior infection. VE remained relativel