Direct impact of COVID-19 vaccination in Chile: averted cases, hospitalizations, ICU admissions, and deaths

Abstract

Background: Chile rapidly implemented an extensive COVID-19 vaccination campaign, deploying a diversity of vaccines with a strategy that prioritized the elderly and individuals with comorbidities. This study aims to assess the direct impact of vaccination on the number of COVID-19 related cases, hospital admissions, ICU admissions and deaths averted during the first year and a half of the campaign.

Methods: Via Chile's transparency law, we obtained access to weekly event counts categorized by vaccination status and age. Integrating this data with publicly available census and vaccination coverage information, we conducted a comparative analysis of weekly incidence rates between vaccinated and unvaccinated groups from December 20, 2020 to July 2, 2022 to estimate the direct impact of vaccination in terms of the number of cases, hospitalizations, ICU admissions and deaths averted, using an approach that avoids the need to explicitly specify the effectiveness of each vaccine deployed.

Results: We estimated that, from December 20, 2020 to July 2, 2022 the vaccination campaign directly prevented 1,030,648 (95% Confidence Interval: 1,016,975-1,044,321) cases, 268,784 (95% CI: 264,524-273,045) hospitalizations, 85,830 (95% CI: 83,466-88,194) ICU admissions and 75,968 (95% CI: 73,909-78,028) deaths related to COVID-19 among individuals aged 16 years and older. This corresponds to a reduction of 26% of cases, 66% of hospital admissions, 70% of ICU admissions and 67% of deaths compared to a scenario without vaccination. Individuals 55 years old or older represented 67% of hospitalizations, 73% of ICU admissions and 89% of deaths related to COVID-19 prevented.

Conclusions: This study highlights the role of Chile's vaccination campaign in reducing COVID-19 disease burden, with the most substantial reductions observed in severe outcomes.

Keywords: Averted events; COVID-19; Cases averted; Deaths averted; Hospitalizations averted; ICU admissions averted; SARS-CoV-2; Vaccine.

Fig. 1

Temporal trends of COVID-19 related cases, hospitalizations, ICU admissions and deaths in Chile. The gray lines represent daily data, while the black lines show the 7-day rolling mean. The horizontal arrow indicates the period of study (from the beginning of the vaccination campaign on December 20, 2020, to July 2, 2022). The vertical dotted line marks the start of the vaccination campaign. The colors represent the time intervals during which each variant was prevalent. Note that healthcare facilities only started recording data sometime after the pandemic began

Fig. 2

Cumulative proportion of the population vaccinated by age and each week in Chile

Fig. 3

Cumulative averted events in individuals 16 years of age and older in Chile. Each plot represents respectively the cumulative number of cases, hospital admissions, ICU admissions and deaths related to COVID-19 averted between December 20, 2020, and July 2, 2022, due to vaccination against COVID-19