The effect of SARS-CoV-2 vaccination on post-acute COVID-19 syndrome (PASC): A prospective cohort study 8 253 between vaccinated cases and unvaccinated controls matched by age, sex, obesity status and months since illness onset. Additionally, vaccination had no effect on the odds of full recovery from PASC within 3 months from vaccination or matched time-point. Given the limited sample size of our matched analysis, these findings do not fully exclude a beneficial effect but do suggest that such an effect is unlikely to be substantial. Larger studies of different designs demonstrate inconsistent results, which may in part be due to differences in selection of study participants. For example, a large study (more than 450 matched pairs) reported a doubling in remission rate among vaccinated cases compared to unvaccinated controls within 120 days of follow-up [5]. However, this study suffers from selection bias, having recruited self-referred patients with PASC, and non-hospitalised patients (91.1% of participants) and women (80.5% of participants) were overrepresented, limiting generalisability of these results. Similarly, a large nationwide survey from the UK, which also included almost exclusively non-hospitalised participants with PASC, reported a small but statistically significant reduction in the odds of reporting PASC symptoms following each vaccination[17]. In contrast, other large studies corroborated the findings in our study, reporting no difference in PASC symptoms between unvaccinated and vaccinated participants [18, 19]. Overall, these conflicting results highlight the importance of prospective population-based cohorts that follow COVID-19 patients at all levels of disease severity from illness onset onwards. Vaccination remains one of the most important public health tools to avert both short- and long-term COVID-19 morbidity, and care should be taken to ensure any lack of therapeutic effect does not fuel vaccine hesitancy among PASC patients [20, 21]. Our observed lack of association between vaccination and PASC is further underscored by our neutralizing antibody analysis and the mostly lacking role of SARS-CoV-2 specific humoral responses in PASC. We did not observe an association between early (30-60 days post-illness onset) virus binding and neutralising antibody titers and the development of PASC overall, nor among PASC participants who experienced moderate COVID-19. When restricting our analyses to those with mild COVID-19, however, participants who developed PASC exhibited higher early RBD-binding antibody titers than those who did not. Importantly, neutralising IgG levels remained unchanged between PASC and non-PASC participants with mild COVID-19. These results seem to conflict with a recent report suggesting lower early IgM and IgG3 titers in PASC patients[6] but mirror a recent prospective Norwegian study of mainly non-hospitalised, mild COVID-19 patients[22]. Similar to our findings, the latter study found that spike-binding IgG titers 2 months after infection were associated with a higher number of symptoms at 6 months (aHR 1.25 [1.01–1.56], p=0.037) [22], also when adjusting for confounding factors such as COVID-19 severity. These higher IgG levels
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