COVID-19 vaccine effectiveness and hybrid immunity in the respiratory season of 2022-23 in Hungary

Abstract Background There has been an increase in COVID-19 vaccine hesitancy among the general population, accompanied by a decline in confidence that vaccines provide adequate protection. We estimated the effectiveness of the COVID-19 vaccines (CVE) and hybrid immunity against medically attended COVID-19 during the 2022-2023 respiratory season in Hungary. Methods We conducted a test-negative design study involving 68 GPs. Patients aged ≥18 years presenting with acute respiratory infection were swabbed. Cases and controls were patients testing positive and negative for SARS-CoV-2 by RT-PCR, respectively. Exposure was defined as having received at least one COVID-19 booster dose, taking into account the time since the last vaccination. CVE was estimated using logistic regression, adjusted for symptom onset date, age, chronic condition and sex. Results We included 247 cases and 1073 controls in the analysis. 196 samples were sequenced, and Omicron BA.5, BQ.1 and XBB.1 were the most frequent sub-variants. The CVE was 52.9% (95% CI: 15.2-73.9%), and 72.3% (95% CI: 32.0-88.7%) in the 18-59, and 60+-year-old population who received the final dose within the past year, respectively. Self-reported COVID-19 in the previous 60-365 days did not confer protection against reinfection, however, when combined 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 Booster vaccination within one year after the last dose confers significant protection against symptomatic infection, particularly among the elderly. Those who have previously been infected with SARS-CoV-2 may also benefit from booster vaccinations. Key messages • COVID-19 booster campaigns must be intensified, focusing mainly on the elderly. • Providing clear guidance on the timing and target groups of vaccination and emphasising the benefits of vaccination can help to achieve higher coverage.