The study, utilizing data from over 20 million participants, demonstrates that COVID-19 vaccines consistently prevent long COVID symptoms in adults. Meta-analytic calibrated substitution hazard ratios (SHRs) for long COVID symptoms were 0.54, 0.48, 0.71, and 0.59 across four datasets from CPRD GOLD, CPRD AURUM, SIDIA, and CORIVA, respectively. Additionally, vaccination with any first dose of a COVID-19 vaccine (ChAdOx1, BNT162b2, and mRNA-1273) was associated with a reduced risk of post-acute heart failure, venous thromboembolism, and arterial thrombosis. The study applied federated analytics to Norwegian Linked Health Registries, covering 5.4 million inhabitants, and generated four study cohorts based on age and health conditions. The results showed that vaccination reduced the risk of long COVID symptoms and post-COVID complications, consistent with findings from other countries. Sensitivity analyses and different methods confirmed the robustness of the findings. The study also highlighted the use of federated analytics for cross-border data analysis and the generalizability of previous publications.The study, utilizing data from over 20 million participants, demonstrates that COVID-19 vaccines consistently prevent long COVID symptoms in adults. Meta-analytic calibrated substitution hazard ratios (SHRs) for long COVID symptoms were 0.54, 0.48, 0.71, and 0.59 across four datasets from CPRD GOLD, CPRD AURUM, SIDIA, and CORIVA, respectively. Additionally, vaccination with any first dose of a COVID-19 vaccine (ChAdOx1, BNT162b2, and mRNA-1273) was associated with a reduced risk of post-acute heart failure, venous thromboembolism, and arterial thrombosis. The study applied federated analytics to Norwegian Linked Health Registries, covering 5.4 million inhabitants, and generated four study cohorts based on age and health conditions. The results showed that vaccination reduced the risk of long COVID symptoms and post-COVID complications, consistent with findings from other countries. Sensitivity analyses and different methods confirmed the robustness of the findings. The study also highlighted the use of federated analytics for cross-border data analysis and the generalizability of previous publications.