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

Barandalla, Ignacio; Alvarez, Carmen; Barreiro, Pablo; de Mendoza, Carmen; González-Crespo, Rubén; Soriano, Vicente

Background The advent of SARS-CoV-2 vaccines has been associated with a significant decline in COVID-19 hospitalizations and deaths. However, little is known about the benefits experienced by different population groups and/or using distinct vaccines. Methods We analyzed the Spanish public registry for associations between calendar vaccination scale up and incidence of COVID-19 hospitalizations by age, gender 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 exponentially increased with age, on average 71.5% for each decade older. Overall individuals older than 60 years-old accounted for 65% of all COVID-19 hospitalizations. Speedy vaccination rollout since the end of 2020 with prioritization of the elderly groups resulted in a rapid drop of COVID-19 hospitalizations since February 2021. The benefit was already noticed 3-4 weeks after the first dose, regardless vaccine modality. Conclusions COVID-19 hospitalizations increased exponentially with age in all three peaks of SARS-CoV-2 infection in Spain. Early massive vaccination of people above 60-years precluded a fourth wave of COVID-19 hospitalizations during the spring of 2021.