Ulrike Baum, Eero Poukka, Tuija Leino, Hanna Nohynek, Arto A. Palmu: High vaccine effectiveness against severe Covid-19 in the elderly in Finland before and after the emergence of Omicron [preprint], in: medRxiv (March 13, 2022), online in: https://doi.org/10.1101/2022.03.11.22272140.
The elderly are highly vulnerable to severe Covid-19. Waning immunity and emergence of Omicron have caused concerns about reduced effectiveness of Covid-19 vaccines. The objective was to estimate vaccine effectiveness (VE) against severe Covid-19 among the elderly.
This nationwide, register-based cohort study included all residents aged 70 years and over in Finland. The follow-up started on December 27, 2020, and ended on February 19, 2022. The study outcomes were Covid-19-related hospitalization and intensive care unit (ICU) admission timely associated with SARS-CoV-2 infection. VE was estimated as 1 minus the hazard ratio comparing the vaccinated and unvaccinated and taking into account time since vaccination. Omicron-specific VE was evaluated as the effectiveness observed since January 1, 2022.
The cohort included 897,932 individuals. Comirnaty (BioNTech/Pfizer) VE against Covid-19-related hospitalization was 93% (95% confidence interval [CI], 90%–95%) and 87% (84%–89%) 14–90 and 91–180 days after the second dose; VE increased to 96% (95%–97%) 14–60 days after the third dose. VE of other homologous and heterologous 3-dose series was similar. Protection against severe Covid-19 requiring ICU treatment was even better. Since January 1, 2022, Comirnaty VE was 91% (95% CI, 79%–96%) and 76% (56%–86%) 14–90 and 91–180 days after the second and 95% (94%–97%) 14–60 days after the third dose.
VE against severe Covid-19 is high among the elderly. It waned slightly after 2 doses, but a third restored the protection. VE against severe Covid-19 remained high even after the emergence of Omicron.
Competing Interest Statement
No financial conflicts related to the current work. Finnish Institute for Health and Welfare (Terveyden ja hyvinvoinnin laitos, THL) conducts Public-Private Partnership with vaccine manufacturers and has received research funding from Sanofi Inc., Pfizer Inc., and GlaxoSmithKline Biologicals SA for non-COVID-19-related studies. AAP has been an investigator in these studies but has received no personal remuneration.
No external funding. This study was funded by the Finnish Institute for Health and Welfare (THL).