Effectiveness of the vaccine against COVID-19 in Mexico City

Introduction: The COVID-19 pandemic had a significant impact on public health in Mexico, with millions of confirmed cases and hundreds of thousands of deaths. Mass vaccination was implemented as a response, aiming to reduce the mortality rate. Objective: To evaluate the effectiveness of COVID-19 vaccination in Mexico City by comparing the lethality of the first wave of infections (unvaccinated population) with the third wave (predominantly vaccinated population). Material and Methods: This is a retrospective observational study that utilized official data from the Mexican Ministry of Health, covering a total of 834,792 confirmed cases in Mexico City. Cases of patients under 18 and over 85 years old were excluded. A logistic regression model was applied, with lethality as the response variable, controlling for age, sex, and comorbidities. Results: The analysis showed that vaccination significantly reduced the probability of death from COVID-19. However, the protective effect diminished with increasing age. Interactions between age and vaccination were statistically significant, indicating a decrease in efficacy with older age. Conclusions: COVID-19 vaccination in Mexico City demonstrated a positive effect in reducing lethality. However, its effectiveness decreases with age, highlighting the need for booster strategies and further studies to assess other potential confounding factors, such as virus variants and hospital pressure during different COVID-19 infection waves.