OBJECTIVES: We aimed to assess the effectiveness of COVID-19 vaccines in preventing laboratory-confirmed COVID-19 hospitalizations and deaths among individuals aged 18 years and older in Colombia.

METHODS: A case-control study was conducted utilizing two control groups: 1. Individuals with Covid 19 - like symptoms plus negative COVID-19 tests. 2. Individuals with no Covid 19 like symptoms. Cases were defined as any person with Covid 19 like symptoms plus a Covid 19 test positive (PCR or rapid test). Cases and controls were obtained from two health centers: the National University Hospital (HUN) and Gestión Salud IPS. Clinical data were obtained from medical records between January 2021 and June 2022 and vaccination information was obtained from PAIWEB.

RESULTS: A total of 705 patients were enrolled in the study, consisting of 197 cases and 508 controls. Among the cases, 137 (69.5%) were unvaccinated, compared to 406 (79.9%) in the control group. Primary doses of mRNA vaccines were most commonly administered (4.6% in cases and 2.2% in controls). The adjusted analysis revealed that the effectiveness of the second dose of mRNA vaccines was 14% (95% CI, -162 to 72).

CONCLUSIONS: Due to the limited sample size, the study lacked adequate statistical power to identify significant differences in vaccine effectiveness against COVID-19. Therefore, it is recommended to conduct further research studies with larger sample sizes.