Importance: Existing systematic literature reviews (SLRs) on COVID 19 vaccine effectiveness (VE) against post COVID 19 conditions (PCC) document high heterogeneity across studies, but have not compared VE across design features known to impact PCC burden or VE against other COVID 19 endpoints. Objective: This SLR summarizes the evidence across studies among predominately adults that report an adjusted measure of association for the relationship between vaccination and PCC, by timing of vaccination relative to infection or PCC onset and across different study characteristics. Evidence review: A comprehensive search strategy was developed within the OVID platform across EMBASE, MEDLINE and Evidence Based Medicine reviews, and supplemented with WHO COVID library and Google Scholar searches, to collate evidence on vaccination and PCC published or posted as pre prints between January 1st, 2020 and July 18th, 2023. JBI Critical Appraisal Checklists were used to assess each study's risk of bias. Findings: This review included 97 studies and synthesized results from 56 studies with low risk of bias that reported adjusted measures for the association between vaccination and PCC. Overall, 77% of pre infection adjusted VE (aVE) estimates (vs. unvaccinated) were statistically significant (range: 7% to 95%), 80% of estimates reflecting a mix of those vaccinated before and after infection were statistically significant (range: 62% to 73%), one of five estimates reflecting vaccination after PCC onset was statistically significant (aVE=41%), 43% of post infection vaccination estimates were statistically significant (two were protective [range: 28% to 40%] and one was not [aVE= minus 47%]), and 46% of estimates not specifying vaccination timing were statistically significant (23 were protective [range: 29% to 75%] and one was not [aVE= minus 132%]). Statistically significant pre-infection aVE estimates were slightly higher for mRNA (range: 14% to 84%) than non mRNA vaccines (range: 16% to 38%) and aVE ranges during (4 studies; range: 10% to 70%) and before Omicron predominance (10 studies; range: 7% to 50%) overlapped. Pre-infection vaccination was protective regardless of vaccine type, number of doses received, PCC definition, predominant variant, and severity of acute infections included. Conclusions and Relevance: Collectively our findings suggest that COVID-19 vaccination received prior to SARS CoV 2 infection reduces the subsequent risk of developing PCC regardless of the predominant variant circulating.
