Figure 2.

The adjusted hazard ratio (aHR) estimates for (A) COVID-19-associated mortality and (B) all-cause mortality by vaccination with an mRNA booster among all individuals living in Norway with a valid national identity number and aged ≥75 years. Fourth dose, >7 days after a fourth COVID-19 vaccine dose was given with either a monovalent or bivalent (BA.1 or BA.4–5) vaccine. ≥24 weeks since the third dose was used as reference level. The Cox proportional hazard model is stratified for age, sex, risk group, resident in long-term care facility and county of residence. Due to the recent introduction of the BA.1 and BA.4–5 vaccines, estimates could only be calculated for the monovalent vaccines for all vaccination statuses