Waning protection after vaccination and prior infection against COVID-19-related mortality over 18 months

Objectives: Evidence on waning patterns in protection from vaccine-induced, infection-induced, and hybrid immunity against death is scarce. The aim of this study is to assess the temporal trends in protection against mortality.Methods: Population-based case-control study nested in the total population of Scania Region, Sweden using individual-level registry data of COVID-19-related deaths (<30 days after positive SARS-CoV-2 test) between 27 December 2020 and 3 June 2022. Controls were matched for age, sex, and index date. Conditional logistic regression was used to estimate the preventable fraction (PF) from vaccination (PFvac corresponding to vaccine effectiveness; >= 2 vaccine doses vs. 0 doses), prior infection (PFinf), and hybrid immunity (PFhybrid). PF was calculated as one minus odds ratio. Models were adjusted for comorbidities, long-term care facility residence, prior infection (for PFvac), country of birth, socio-economic conditions, and time since last vaccination (for PFinf).Results: In total, 14 936 individuals (1440 COVID-19-related deaths and 13 496 controls) were included in the case-control analyses (45% females, median age: 84 years). PFvac was above 90% during the first month after vaccination, regardless of the number of vaccine doses. After 6 months, PFvac of two doses waned to 34% (95% CI: -30% to 66%). PFinf for people surviving a SARS-CoV-2 infection waned from 88% (-16% to 99%) 3 months after infection to 62% (34-79%) after 9 months. No differences in waning patterns in PF(vac )were seen between virus variants, gender, and age.Discussion: Given the waning of protection against death, continuous surveillance of population immunity status, particularly among the most vulnerable population groups, could help to further fine-tune vaccination recommendations. Dominik Dietler, Clin Microbiol Infect 2023;29:1573 (c) 2023 The Author(s). Published by Elsevier Ltd on behalf of European Society of Clinical Microbiology and Infectious Diseases. This is an open access article under the CC BY license (http://creativecommons. org/licenses/by/4.0/).

Automated summary

This study assesses the temporal trends in protection against mortality and finds that the protection from vaccine-induced and infection-induced immunity decreases over time. Continuous surveillance of population immunity status, especially among vulnerable populations, is recommended to further refine vaccination recommendations.