Effectiveness of mRNA booster doses in preventing infections and hospitalizations due to SARS-CoV-2 and its dominant variant over time in Valencian healthcare workers, Spain

Natali Jiménez-Sepúlveda; Paula Gras-Valentí; Pablo Chico-Sánchez; José Miguel Castro-García; Elena Ronda-Pérez; Hermelinda Vanaclocha; Salvador Peiró; Javier S Burgos; Ana Berenguer; David Navarro; José Sánchez-Payá; Valencian vaccine research program ProVaVac study group

doi:10.1016/j.vaccine.2024.05.011

Effectiveness of mRNA booster doses in preventing infections and hospitalizations due to SARS-CoV-2 and its dominant variant over time in Valencian healthcare workers, Spain

Vaccine. 2024 May 16:S0264-410X(24)00557-7. doi: 10.1016/j.vaccine.2024.05.011. Online ahead of print.

Affiliations

¹ Epidemiology Unit, Preventive Medicine Service, Dr. Balmis General University Hospital, Alicante Institute for Health and Biomedical Research (ISABIAL), Alicante, Spain.
² Epidemiology Unit, Preventive Medicine Service, Dr. Balmis General University Hospital, Alicante Institute for Health and Biomedical Research (ISABIAL), Alicante, Spain; Preventive Medicine and Public Health Area, Faculty of Health Sciences, University of Alicante, Alicante, Spain.
³ Epidemiology Unit, Preventive Medicine Service, Dr. Balmis General University Hospital, Alicante Institute for Health and Biomedical Research (ISABIAL), Alicante, Spain; Preventive Medicine and Public Health Area, Faculty of Health Sciences, University of Alicante, Alicante, Spain. Electronic address: pablochico@pablochico.es.
⁴ Thoracic Imaging Division, Saint Michael's Hospital, Toronto, Canada.
⁵ Preventive Medicine and Public Health Area, Faculty of Health Sciences, University of Alicante, Alicante, Spain; Centre of Networked Biomedical Research in Epidemiology and Public Health (CIBERESP), Madrid, Spain.
⁶ General Directorate of Public Health, Department of Health, Valencia Government, Valencia, Spain.
⁷ Foundation for the Promotion of Health and Biomedical Research of the Valencian, Community (FISABIO), Valencia, Spain.
⁸ General Directorate of Research and Healthcare Supervision, Department of Health, Valencia Government, Valencia, Spain.
⁹ General Directorate of Analysis and Public Policy, Valencia Government, Valencia, Spain.
¹⁰ Microbiology Service, Clinic University Hospital, INCLIVA Health Research Institute, Valencia, Spain; Department of Microbiology, School of Medicine, University of Valencia, Valencia, Spain.

PMID: 38760269
DOI: 10.1016/j.vaccine.2024.05.011

Abstract

Objective: This study aimed to evaluate the effectiveness of SARS-CoV-2 mRNA vaccines in preventing infection and hospitalization among healthcare workers (HCWs) in the Valencian Community (Spain), considering vaccination timing, dose number, and predominant variant.

Methods: A test-negative case-control design estimated vaccine effectiveness against symptomatic disease and hospitalization due to SARS-CoV-2. HCWs who underwent PCR or antigen testing for SARS-CoV-2 from January 2021 to March 2022 were included. Cases had a positive diagnostic test, while controls had negative tests. Adjusted vaccine effectiveness (aVE) was calculated using the formula: aVE = (1 - Odds ratio) × 100.

Results: During the Delta variant's predominance, aVE against infection within 12-120 days post-second dose was 64.8 % (BNT162b2) and 59.4 % (mRNA-1273), declining to 21.2 % and 42.2 %, respectively, after 120 days. For the Omicron variant, aVE within 12-120 days post-second dose was 61.1 % (BNT162b2) and 85.1 % (mRNA-1273), decreasing to 36.7 % and 24.9 %, respectively, after 120 days. After a booster dose of mRNA-1273, aVE was 64.0 % (BNT162b2 recipients) and 65.9 % (initial mRNA-1273 recipients). Regardless of variant, aVE for hospitalization prevention after 2 doses was 87.0 % (BNT162b2) and 89.0 % (mRNA-1273).

Conclusion: The administration of two doses of Moderna-mRNA-1273 against SARS-CoV-2 in HCWs proved to be highly effective in preventing infections and hospitalizations in the first 120 days after the second dose during the predominance of the Omicron variant. The decline in VE after 120 days since the administration of the second dose was significantly restored by the booster dose administration. This increase in VE was greater for the Pfizer vaccine. COVID-19 hospitalization prevention remained stable with both mRNA vaccines throughout the study period.

Keywords: COVID-19; Case-control; Healthcare worker; Infection prevention and control; SARS-CoV-2; SARS-CoV-2 vaccine; SARS-CoV-2 variants.