Vaccine Effectiveness against GP-Attended Symptomatic COVID-19 and Hybrid Immunity among Adults in Hungary during the 2022–2023 Respiratory Season Dominated by Different SARS-CoV-2 Omicron Subvariants

TL;DR

This study found that booster vaccines in Hungary were moderately effective against Omicron subvariants in older adults, and combining prior infection with vaccination significantly reduced reinfection risk.

Contribution

The study evaluates hybrid immunity and booster effectiveness in a population with low vaccination coverage and high natural immunity.

Findings

Booster vaccination was 56.8% effective in adults aged 60+ against Omicron subvariants.

Hybrid immunity reduced reinfection risk by 63.0% in 18–59-year-olds and 87.6% in 60+ adults.

Prior infection alone did not protect against reinfection without vaccination.

Abstract

Hungary provides the opportunity to evaluate the effectiveness of COVID-19 vaccination in a setting where naturally acquired immunity and hybrid immunity are likely to play a greater role due to suboptimal vaccination coverage. Methods: A test-negative study was conducted during the 2022–2023 respiratory season at the primary care level to determine the effectiveness of at least one COVID-19 booster dose in preventing medically attended symptomatic RT-PCR-confirmed SARS-CoV-2 infection in adults. Unvaccinated patients were used as a reference group. Results: A total of 247 cases and 1073 controls were included in the analysis. CVE was 56.8% (95% CI: 11.9–78.8%) in the population aged 60 years and older and 2.3% (95% CI: −50.0–36.3%) in the younger adults against COVID-19 caused by Omicron subvariants, mainly BA.5, BQ.1, and XBB.1. Self-reported COVID-19 in the 60–365 days prior to the current illness did not confer protection against reinfection without vaccination, but together with booster vaccination, it reduced the risk of COVID-19 by 63.0% (95% CI: −28.0–89.3%) and 87.6% (95% CI: 26.4–97.9%) among the 18–59 and 60+ age groups, respectively. Conclusions: CVE against COVID-19 was moderately high in the 60+ age groups. Because of the benefit of hybrid immunity, persons with previous SARS-CoV-2 infection should still be considered for vaccination campaigns.

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