Background: World Health Organization approved vaccines have demonstrated relatively high protection against moderate to severe COVID-19. Prospective vaccine effectiveness (VE) designs with first-hand data and population-based controls are nevertheless rare. Neighborhood compared to hospitalized controls, may differ in compliance to non-pharmacuetical interventions (NPI) compliance, which may influence VE results in real-world settings. We aimed to determine VE against COVID-19 intensive-care-unit (ICU) admission using hospital and community-matched controls in a prospective design. Methods: We conducted a multicenter, observational study of matched cases and controls (1:3) in adults ≧18 years of age from May to July 2021. For each case, a hospital control and two community controls were matched by age, gender, and hospital admission date or neighborhood of residence. Conditional logistic regression models were built, including interaction terms between NPIs, lifestyle behaviors, and vaccination status; the model's β coefficients represent the added effect these terms had on COVID-19 VE. Results: Cases and controls differed in several factors including education level, obesity prevalence, and behaviors such as compliance with routine vaccinations, use of facemasks, and routine handwashing. VE was 98·2% for full primary vaccination and 85·6% for partial vaccination when compared to community controls, and somewhat lower, albeit not significantly, compared to hospital controls. A significant added effect to vaccination in reducing COVID-19 ICU admission was regular facemask use and VE was higher among individuals non-compliant with the national vaccine program, and/or tonroutine medical visits during the prior year. Conclusion: VE against COVID-19 ICU admission in this stringent prospective case-double control study reached 98% two weeks after full primary vaccination, confirming the high effectiveness provided by earlier studies. Face mask use and hand washing were independent protective factors, the former adding additional benefit to VE. VE was significantly higher in subjects with increased risk behaviors.
Bibliographical noteFunding Information:
We would like to thank the following medical students from the Universidad de los Andes and the Universidad de Chile for their work recruiting and interviewing study participants: Almendra Fernanda Gómez Berrios, Diego Ignacio Muñoz Salamanca, Ximena Aguilera, Andrés Ignacio Rojas Liberona, Nayareth de los Angeles Negrón Monr, Javiera Carstens Taub, Sofia Barros Correia Mendes, Cristóbal Edwards Latorre, Macarena Shejade Sirhan, Martín Eduardo Tolosa Titichoca, and Álvaro Kompatzki. We would like to thank Manuel Diaz and Sebastian Sepulveda from the Servicio de Salud Metropolitano Central for their support in georeferencing the residences of cases and their possible community controls. Finally, we would like to express our gratitude to the Servicio de Salud Metropolitano Central, the municipal corporations of Maipu and Santiago, Hospital de Urgencia Asistencia Pública, and Hospital El Carmen Dr. Luis Valentín Ferrada for their support of the study. The study received funding support from the Confederación de la Producción y el Comercio (CPC) to help support staff. The study database is available from the authors upon reasonable request and with the permission of Cinthya Urquidi, the first author of the study.
© 2023 Elsevier Ltd
- Non-pharmacological intervention
- Risk factors
- Vaccine effectiveness