LAUSR

Background: Waning immunity following administration of mRNA based COVID-19 vaccines remains a concern for many health systems. We undertook a study of SARS-CoV-2 infections, with and without requirement for intensive care to shed more light on the duration of vaccine effectiveness for protection against the need for intensive care. Methods: We used a matched case-control study design with the study base being all individuals with first infection with SARS-CoV-2 reported in the State of Qatar between 1 Jan 2021 and 20 Feb 2022. Cases were those requiring intensive care while controls were those who recovered without need for intensive care. Vaccine effectiveness against requiring intensive care and number needed to vaccinate (NNV) to prevent one more case of COVID-19 requiring intensive care were computed for the mRNA (BNT162b2 / mRNA-1273) vaccines. Results: Vaccine effectiveness against requiring intensive care was 59% (95% confidence interval [CI], 50 to 76) between the first and second dose and strengthened to 89% (95% CI, 85 to 92) between the second dose and 4 months post the second dose in persons who received a primary course of the vaccine. There was no waning of vaccine effectiveness in the period from 4 to 12 months after the second dose. Conclusions: This study demonstrates that vaccine effectiveness against requiring intensive care remains robust till at least 12 months after the second dose of mRNA based vaccines.