Early impact of COVID-19 vaccination on older populations in four countries of the Americas, 2021

Objective. To estimate the early impact of coronavirus disease 2019 (COVID-19) vaccination on cases in older populations in four countries (Chile, Colombia, Guatemala, and the United States of America), and on deaths in Chile and Guatemala.Methods. Data were obtained from national databases of confirmed COVID-19 cases and deaths and vac-cinations between 1 July 2020 and 31 August 2021. In each country, pre-and post-vaccination incidence ratios were calculated for COVID-19 cases and deaths in prioritized groups (50-59, 60-69, and & GE;70 years) compared with those in the reference group (<50 years). Vaccination effect was calculated as the percentage change in incidence ratios between pre-and post-vaccination periods.Results. The ratio of COVID-19 cases in those aged & GE;50 years to those aged <50 years decreased signifi-cantly after vaccine implementation by 9.8% (95% CI: 9.5 to 10.1%) in Chile, 22.5% (95% CI: 22.0 to 23.1%) in Colombia, 20.8% (95% CI: 20.6 to 21.1%) in Guatemala, and 7.8% (95% CI: 7.6 to 7.9%) in the USA. Reduc-tions in the ratio were highest in adults aged & GE;70 years. The effect of vaccination on deaths, with time lags incorporated, was highest in the age group & GE;70 years in both Chile and Guatemala: 14.4% (95% CI: 11.4 to 17.4%) and 37.3% (95% CI: 30.9 to 43.7%), respectively. Conclusions. COVID-19 vaccination significantly reduced morbidity in the early post-vaccination period in targeted groups. In the context of a global pandemic with limited vaccine availability, prioritization strategies are important to reduce the burden of disease in high-risk age groups.