Previous SARS-CoV-2 infections and their impact on the protection from reinfection during the Omicron BA.5 wave - a nested case-control study among vaccinated adults in Sweden

Fredrik Kahn; Carl Bonander; Mahnaz Moghaddassi; Claus Bohn Christiansen; Louise Bennet; Ulf Malmqvist; Malin Inghammar; Jonas Björk

doi:10.1016/j.ijregi.2024.02.004

Previous SARS-CoV-2 infections and their impact on the protection from reinfection during the Omicron BA.5 wave - a nested case-control study among vaccinated adults in Sweden

IJID Reg. 2024 Feb 28:10:235-239. doi: 10.1016/j.ijregi.2024.02.004. eCollection 2024 Mar.

Authors

Fredrik Kahn¹, Carl Bonander², Mahnaz Moghaddassi³, Claus Bohn Christiansen⁴, Louise Bennet^{5

6}, Ulf Malmqvist⁶, Malin Inghammar¹, Jonas Björk^{6

7}

Affiliations

¹ Department of Clinical Sciences Lund, Section for Infection Medicine, Lund University, Lund, Sweden.
² School of Public Health and Community Medicine, Institute of Medicine, University of Gothenburg, Gothenburg, Sweden.
³ Department of Clinical Sciences Malmö, Section for Social Medicine and Global Health, Lund University, Malmö, Sweden.
⁴ Department of Clinical Microbiology and Infection Prevention and Control, Skåne University Hospital, Lund, Sweden.
⁵ Department of Clinical Sciences Malmö, Section for Family Medicine, Lund University, Malmö, Sweden.
⁶ Clinical Studies Sweden, Forum South, Skåne University Hospital, Lund, Sweden.
⁷ Department of Laboratory Medicine, Division of Occupational and Environmental Medicine, Lund University, Lund, Sweden.

Abstract

Objectives: We evaluated the protection afforded by SARS-CoV-2 infection-induced immunity against reinfection among working-age vaccinated individuals during a calendar period from June to December 2022 when Omicron BA.5 was the dominating subvariant in Scania County, Sweden.

Methods: The study cohort (n = 71,592) mainly consisted of health care workers. We analyzed 4144 infected cases during the Omicron BA.5 dominance and 41,440 sex- and age-matched controls with conditional logistic regression.

Results: The average protection against reinfection was marginal (16%, 95% confidence interval [CI] 7-23%) during the study period but substantially higher for recent infections. Recent infection (3-6 months) with Omicron BA.2 and BA.5 offered strong protection (86%, 95% CI 68-94% and 78%, 95% CI 69-84%), whereas more distant infection (6-12 months) with Omicron BA.1, BA.2, and the variants before Omicron offered marginal or no protection.

Conclusions: These findings suggest that infection-induced immunity contributes to short-term population protection against infection with the subvariant BA.5 among working-age vaccinated individuals but wanes considerably with time, independent of the virus variant.

Keywords: Epidemiological surveillance; SARS-CoV-2 infection; Variant of concern.