The effect of SARS-CoV-2 vaccination on post-acute COVID-19 syndrome (PASC): A prospective cohort study 8 249 Changes to PASC symptoms following vaccination Among participants with at least 3 months of follow-up after illness onset who developed PASC (n=186), 36 follow-up period pairs were exact matched, originating from 36 vaccinated cases and 32 unvaccinated controls (4 participants contributed two unvaccinated followup periods) (Supplementary Table S1; Supplementary Figure S1a). Median length of follow-up after matching did not differ between vaccinated (3 months [IQR=3-3]) and unvaccinated (3 months [IQR 1-3]) groups. There was no statistically significant difference in the mean total number of symptoms reported between unvaccinated and vaccinated participants at each month during the 3 months following the matched time-point (Figure 1). The odds of recovery from PASC did not differ between vaccinated (6 recovery events) and unvaccinated participants (4 recovery events) (OR 1.57 [95%CI 0.46-5.84], p=0.596) in the follow-up period up to 3 months following the matched time-point. Overall, among all participants with PASC at first vaccination, the vast majority reported that they had the feeling that their PASC symptoms had not changed within a month after first vaccination, regardless of initial COVID-19 severity (Supplementary Figure S3). Figure 1. Mean number of symptoms during exposure-matched unvaccinated and vaccinated follow-up intervals, among participants with PASC Black vertical bands represent 95% CIs, which were calculated from bootstrapped variance estimates to ensure that variance was independent and identically distributed across participants. Time represents nearest month since first vaccination (for vaccinated participants) or matched time-point (for unvaccinated participants) that symptom survey was completed. P-values were obtained from the Wald χ2 test comparing the mean number of symptoms in unvaccinated and vaccinated time-intervals at each month of follow-up, with bootstrapped variance estimates. PASC = Post-acute sequelae of COVID-19.
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