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

## TL;DR

Having early COVID-19 infection may reduce the severity of later Omicron infections, particularly if the initial infection occurred 14–26 months before.

## Contribution

The study shows that early SARS-CoV-2 infection within a specific timeframe is associated with reduced severity of subsequent Omicron infections.

## Key findings

- Early SARS-CoV-2 infection 14–26 months prior was linked to less impact on daily living during Omicron infection.
- Infections occurring more than 26 months prior did not show a similar protective effect.
- 68% of Omicron patients had prior confirmed SARS-CoV-2 infection in 2020.

## 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).