Vaccine effectiveness in reducing COVID-19-related hospitalization after a risk-age-based mass vaccination program in a Chilean municipality: A comparison of observational study designs

Cinthya Urquidi; Alejandro Sepúlveda-Peñaloza; María T Valenzuela; Alexander Ponce; Verónica Menares; Claudia P Cortes; Rosana Benítez; Emilio Santelices; Renato Anfossi; Andrea Moller; María E Santolaya

doi:10.1016/j.vaccine.2024.05.002

Vaccine effectiveness in reducing COVID-19-related hospitalization after a risk-age-based mass vaccination program in a Chilean municipality: A comparison of observational study designs

Vaccine. 2024 May 14:S0264-410X(24)00538-3. doi: 10.1016/j.vaccine.2024.05.002. Online ahead of print.

Affiliations

¹ Department of Epidemiology, Faculty of Medicine, Universidad de Los Andes, Santiago, Chile.
² Information Technology Services, Development Department, Universidad de O'Higgins, Rancagua, Chile.
³ Hospital Regional Libertador Bernardo ÓHiggins, Rancagua, Chile.
⁴ Department of Internal Medicine, Faculty of Medicine, Universidad de Chile, Santiago, Chile.
⁵ Infectious Diseases Department, Clínica Dávila, Santiago, Chile.
⁶ Policy and Innovation Center, Universidad de Desarrollo, Santiago, Chile.
⁷ Department of Pediatrics, Hospital Dr. Luis Calvo Mackenna, Faculty of Medicine, Universidad de Chile, Santiago, Chile. Electronic address: msantola@uchile.cl.

PMID: 38749822
DOI: 10.1016/j.vaccine.2024.05.002

Abstract

Background: Case-control studies involving test-negative (TN) and syndrome-negative (SN) controls are reliable for evaluating influenza and rotavirus vaccine effectiveness (VE) during a random vaccination process. However, there is no empirical evidence regarding the impact in real-world mass vaccination campaigns against SARS-CoV-2 using TN and SN controls.

Objective: To compare in the same population the effectiveness of SARS-CoV-2 vaccination on COVID-19-related hospitalization rates across a cohort design, TN and SN designs.

Method: We conducted an unmatched population-based cohort, TN and SN case-control designs linking data from four data sources (public primary healthcare system, hospitalization registers, epidemiological surveillance systems and the national immunization program) in a Chilean municipality (Rancagua) between March 1, 2021 and August 31, 2021. The outcome was COVID-19-related hospitalization. To ensure sufficient sample size in the unexposed group, completion of follow-up in the cohort design, and sufficient time between vaccination and hospitalization in the case-control design, VE was estimated comparing 8-week periods for each individual.

Results: Among the 191,505 individuals registered in the primary healthcare system of Rancagua in Chile on March 1, 2021; 116,453 met the cohort study's inclusion criteria. Of the 9,471 hospitalizations registered during the study period in the same place, 526 were COVID-19 cases, 108 were TN controls, and 1,628 were SN controls. For any vaccine product, the age- and sex-adjusted vaccine effectiveness comparing fully and nonvaccinated individuals was 67.2 (55.7-76.3) in the cohort design, whereas it was 67.8 (44.1-81.4) and 77.9 (70.2-83.8) in the TN and SN control designs, respectively.

Conclusion: The VE of a COVID-19 vaccination program based on age and risk groups tended to differ across the three observational study designs. The SN case-control design may be an efficient option for evaluating COVID-19 VE in real-world settings.

Keywords: COVID-19; Case-control; Cohort study; Mass vaccination; SARS-CoV-2; Test-negative design; Vaccine effectiveness.