Booster vaccination and post-COVID-19 condition during the Omicron variant-dominant wave: a large population-based study.

Objectives: The effect of the COVID-19 booster vaccination and the long-term consequences concerning preventing post-COVID-19 condition (PCC) remains unclear. We aimed to investigate the association of COVID-19 booster vaccination dose and vaccination timing before infection with the risk of PCC during the Omicron variant-dominant wave.

Methods: This population-based study included patients confirmed with COVID-19 (extracted from the Health Center Real-time Information-sharing System) aged 20-69 years, who were infected between 1 July and 31 August 2022. We used a self-report questionnaire to evaluate PCC and extracted information on vaccination from the municipal vaccine registry system. We calculated multiple propensity scores for COVID-19 vaccination status (unvaccinated, 1-2 doses and ≥3 doses) to control for baseline population differences. We then used a logistic regression model with inverse probability weighting to analyse the associations between the number of vaccine doses and the risk of PCC. Additionally, we conducted stratified analysis by gender and subgroup analysis for respiratory and neurological symptoms. Multivariable logistic regression was used to analyse the association between vaccination timing and PCC risk, adjusting for vaccination doses.

Results: Of the 7936 participants with COVID-19 (mean age 42.9 years, 4553 women), 940 (11.8%) had at least 1 PCC. Compared with people unvaccinated, those vaccinated ≥3 times before the infection had a lower probability of PCC with the OR of 0.69 (95% CI: 0.53-0.90), although we detected no association with one or two doses. This association was present in women (≥3 doses vs. unvaccinated OR: 0.70, 95% CI: 0.51-0.95) but not in men. Those vaccinated ≥3 times had fewer neurological symptoms compared with those unvaccinated (OR: 0.61, 95% CI: 0.45-0.83); however, no significant association was found for respiratory symptoms.

Discussion: This study suggests that booster vaccination could lower the risk of PCC.