The impact of the Covid-19 vaccination policy in Mexico. A quasi-experimental effectiveness evaluation of a multi-vaccine strategy

Objective. To assess the impact of a vaccination campaign that administered five different technologies in a middle-income country with one of the largest Covid-19 epidemics. Materials and methods. Using data from Mexico's Epidemiological Surveillance System for Viral Respiratory Disease (Sisver) and the design of the vaccine policy in Mexico as a natural experiment, we applied difference-in-differences econometric methods to assess the strategy's effectiveness on transmission, hospitalizations, and mortality rates among adults 60 to 64 years old in Mexico between April and June 2021. Results. We estimated average effectiveness levels of 60.9% against confirmed cases of Covid-19. Vaccination also decreased hospitalizations and deaths by 62.7 and 62.6%, respectively. After adjusting for vaccination coverage, we found an impact of 79.1, 80.9, and 81.3% reduction in new cases, hospitalizations, and deaths among the vaccinated. Conclusion. Despite the significant progress in our knowledge of Covid-19 vaccination effectiveness, the available evidence relies mostly on experiences from high-income countries. This study contributes to the scientific literature of Covid-19 vaccination effectiveness in a middle-income country with a multi-vaccine scheme.