biostudies-literatureLai FTTFood and Health Bureau of the Government of the Hong Kong Special Administrative Region | Health and Medical Research Fund (HMRF)Food and Health Bureau of the Government of the Hong Kong Special Administrative Region | Health and Medical Research Fund411https://www.ebi.ac.uk/biostudies/studies/S-EPMC8776841biostudies-literatureUnknown13(1)Prior research using electronic health records for Covid-19 vaccine safety monitoring typically focuses on specific disease groups and excludes individuals with multimorbidity, defined as ≥2 chronic conditions. We examine the potential additional risk of adverse events 28 days after the first dose of CoronaVac or Comirnaty imposed by multimorbidity. Using a territory-wide public healthcare database with population-based vaccination records in Hong Kong, we analyze a retrospective cohort of patients with chronic conditions. Thirty adverse events of special interest according to the World Health Organization are examined. In total, 883,416 patients are included and 2,807 (0.3%) develop adverse events. Results suggest vaccinated patients have lower risks of adverse events than unvaccinated inNature communicationsMultimorbidity and adverse events of special interest associated with Covid-19 vaccines in Hong Kong.PMC8776841COVID19F01Chui CSLChan EWYWong ICKHuang LLuo HLai FTTMa TChan EWWLi XLum DHWan EYFLeung JCNWong CKHfalseMultimorbidity and adverse events of special interest associated with Covid-19 vaccines in Hong Kong.Prior research using electronic health records for Covid-19 vaccine safety monitoring typically focuses on specific disease groups and excludes individuals with multimorbidity, defined as ≥2 chronic conditions. We examine the potential additional risk of adverse events 28 days after the first dose of CoronaVac or Comirnaty imposed by multimorbidity. Using a territory-wide public healthcare database with population-based vaccination records in Hong Kong, we analyze a retrospective cohort of patients with chronic conditions. Thirty adverse events of special interest according to the World Health Organization are examined. In total, 883,416 patients are included and 2,807 (0.3%) develop adverse events. Results suggest vaccinated patients have lower risks of adverse events than unvaccinated in2022-01-01T00:00:00Z2022 Jan2025-04-27T03:36:29.399Z2025-04-06T18:54:17.747ZS-EPMC87768413505846310.1038/s41467-022-28068-3