# Temporal Heterogeneous in the Effectiveness of Inactivated CoronaVac and Sinopharm Vaccines Against SARS-CoV-2 Reinfections in China

## TL;DR

This study examines how the effectiveness of inactivated SARS-CoV-2 vaccines changes over time against reinfections in China.

## Contribution

The study reveals the temporal heterogeneity in vaccine effectiveness against SARS-CoV-2 reinfections, particularly with Omicron variants.

## Key findings

- Reinfection risk increased over time since initial infection.
- Two or three vaccine doses offered additional protection for those infected with pre-Omicron variants over a year earlier.
- Vaccines provided limited protection against reinfection for those infected with Omicron variants within a year.

## Abstract

We aimed to understand the temporal dynamics of SARS-CoV-2 reinfection risk and assess the impact of inactivated vaccination on the occurrence of reinfection. We investigated the reinfection risk of SARS-CoV-2 from November 1, 2022, to February 12, 2023, when China rapidly lifted the zero-COVID policy. The study subjects were those who were first infected during the zero-COVID period between January 1, 2020, and October 31, 2022, in Dalian city, China. Among the 1961 previous infections, 126 (6.4%, 95% CI: 5.4, 7.5) were reinfected. The risk of reinfection increased over time since initial infection. Compared with those who did not receive or received one dose of inactivated vaccine, receiving two or three doses was associated with additional protection against reinfection among individuals who were infected with pre-Omicron more than a year earlier, with the OR ranged from 0.33 (95% CI: 0.03, 1.83) to 0.91 (95% CI: 0.22, 3.27). In contrast, no protective effect from two or three doses of vaccines against reinfection was observed among those who were first infected with Omicron variants within a year. Primary or booster vaccination contributed to limited protection against reinfection or symptomatic reinfection among individuals infected with Omicron SARS-CoV-2 within a year. However, a booster dose after 1 year of natural infection may provide additional protection against reinfection.