This study provides the most conclusive evidence to date that infection with the omicron subvariant BA.1 was inherently less deadly than delta when controlling for a number of key covariates. Combining death certification records with molecular surveillance is the main advantage of this study, which avoids previous biases in covid-19 death designations. Accounting for a broad array of standardised covariates, including sociodemographic variables, pre-existing health conditions, and previous immunity, is another strength.