What question did this study set out to answer?

The research aims to assess whether early COVID-19 infections lessen the severity of subsequent Omicron infections.

January 14, 2026Influenza and Other Respiratory Viruses0 citationsOpen Access

Early COVID‐19 and Severity of Subsequent Omicron Infection in Ontario Canada

CKCaroline KasseeSinai Health System ASAltynay ShigayevaSinai Health System ABAndra BaneteUniversity of Toronto

Key Points

The research aims to assess whether early COVID-19 infections lessen the severity of subsequent Omicron infections.
Compared activities of daily living (ADL), healthcare utilization, and illness duration among different COVID-19 history groups.
Categorized participants into three groups: those with early COVID-19 compatible illness, early lab-confirmed COVID-19 14–26 months prior, and those > 26 months prior.
Utilized a sample of 261 patients with laboratory-confirmed Omicron infection.
Among 261 participants, 177 (68%) had COVID-19 in 2020.
Early COVID-19 infection 14–26 months prior was linked to a significant reduction in impact on ADL during the first Omicron infection, with an odds ratio of 0.52.
No significant effect was found for COVID-19 > 26 months prior.

Abstract

ABSTRACT We evaluated whether having early COVID‐19 reduced the severity of subsequent Omicron infection, assessing activities of daily living (ADL), healthcare utilization and illness duration. Comparisons were made between persons with (1) early COVID‐19‐compatible illness with a negative test, (2) early lab‐confirmed SARS‐CoV‐2 14–26 months and (3) early lab‐confirmed SAR‐CoV‐2 > 26 months before Omicron infection. Among 261 patients with laboratory‐confirmed Omicron, 177 (68%) had COVID‐19 in 2020, a median of 793 days (IQR, 659–902) prior to Omicron infection. Compared to no early COVID‐19, COVID‐19 14–26 months, but not > 26 months, before was associated with reduced impact on ADL during first Omicron infection (OR 0.52, 95% CI 0.29–0.93).

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