Effect of COVID-19 vaccination on the risk of developing post-COVID conditions: The VENUS study

Introduction: Post-COVID-19 conditions have emerged as a global health challenge. This study examined the longterm effects of COVID-19 vaccination on the incidence and risk of post-COVID-19 conditions in Japan. Methods: This retrospective cohort study was conducted using a database comprising medical claims, COVID-19 case information, and vaccination records of persons residing in four Japanese municipalities. The cohort included COVID-19 cases diagnosed between August 2020 and December 2022. Participants were classified according to the duration between their most recent COVID-19 vaccination and COVID-19 occurrence (>= 365 days, 150-364 days, and 14-149 days). The incidences of 36 post-COVID-19 conditions were monitored for 3, 5, and 8 months after infection. Cox proportional hazards models were used to calculate the risk of developing each post-COVID-19 condition within 8 months after infection according to vaccination status. Results: From among 84,464 participants, 9642 (11.4 %) developed post-COVID-19 conditions over 8 months. The 8-month risks of developing 28 (including various respiratory conditions, cardiovascular conditions, inflammatory and immune diseases, physical conditions, psychiatric conditions, and endocrine disorders) of the 36 target conditions were significantly lower when individuals had been recently vaccinated (14-149 days) before infection. Conclusions: COVID-19 vaccination can reduce the incidence and risk of post-COVID-19 conditions if administered within 5 months before infection. Despite having the highest mean age and prevalence of comorbidities, individuals who were most recently vaccinated had a lower risk of developing post-COVID-19 conditions. These results provide important evidence for future COVID-19 vaccination strategies.