Statistical explanation of the protective effect of four COVID-19 vaccine doses in the general population

Objectives: To assess the effectiveness of four doses of the vaccine against SARS-CoV-2 in the general population and the impact of this on the severity of the disease by age group. Methods: By using data from the health authority public data base, we build statistical models using R and the GAMLSS library to explain the behavior of new SARS-CoV-2 infections, active COVID-19 cases, ICU bed requirement total and by age group, and deaths at the national level. Results: The four doses of vaccine and at least the interaction between the first and second doses were important explanatory factors for the protective effect against COVID-19. The R-2 for new cases per day was 0.5644 and for occupied ICU beds the R-2 is 0.9487. For occupied ICU beds for >70 years R-2 is 0.9195 and with the interaction between 4 doses as the main factor. Conclusions: Although the increase in the number of vaccine doses did not adequately explain the decrease in the number of COVID-19 cases, it explained the decrease in ICU admissions and deaths nationwide and by age group.