Factors affecting the impact of COVID-19 vaccination on post COVID-19 conditions among adults: A systematic literature review.

This systematic literature review summarizes the evidence across 56 publications and pre-prints (January 2020-July 2023) with low-risk of bias based on JBI critical appraisal, that report adjusted estimates for the relationship between COVID-19 vaccination and Post-COVID-19 Condition (PCC) by timing of vaccination relative to infection or PCC-onset. Comparisons of adjusted vaccine effectiveness (aVE) against ≥1 PCC (vs. unvaccinated) across study characteristics known to impact PCC burden or VE against other COVID-19 endpoints were possible for 31 studies where vaccination preceded infection. Seventy-seven percent of pre-infection aVE estimates were statistically significant (range: 7%-95%). Statistically significant pre-infection aVE estimates were slightly higher for mRNA (range: 14%-84%) than non-mRNA vaccines (range: 16%-38%) and aVE ranges before and during Omicron overlapped. Our findings suggest that COVID-19 vaccination before SARS-CoV-2 infection reduces the risk of PCC regardless of vaccine type, number of doses received, PCC definition, predominant variant, and severity of acute infections included.