Impact of scaling up SARS-CoV-2 vaccination on COVID-19 hospitalizations in Spain

BACKGROUND: The advent of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines has been associated with a significant decline in coronavirus disease 2019 (COVID-19) hospitalizations and deaths. However, little is known about the benefits experienced by different population groups and/or using distinct vaccines. METHODS: The Spanish public registry was analyzed to examine associations between weekly vaccination scale-up and the incidence of COVID-19 hospitalizations by age, sex, and vaccine modality. The study period extended from January 2020 to June 2021. RESULTS: A total of 363 960 COVID-19 hospitalizations were recorded in Spain during the study period, with three peaks in March 2020, November 2020, and January 2021. The incidence of COVID-19 hospitalizations per 100 000 population increased exponentially with age, on average 71.5% for each decade older. Overall, individuals older than 60 years of age accounted for 65% of all COVID-19 hospitalizations. The speedy vaccination rollout since the end of 2020, with prioritization of the elderly groups, resulted in a rapid fall in COVID-19 hospitalizations starting in February 2021. The benefit was already noticed 3–4 weeks after the first dose, regardless of the vaccine modality. CONCLUSIONS: COVID-19 hospitalizations increased exponentially with age in all three peaks of SARS-CoV-2 infection in Spain. Early mass vaccination of people over 60 years of age prevented a fourth wave of COVID-19 hospitalizations during the spring of 2021.