Indirect effectiveness of a novel SARS-COV-2 vaccine (SCB-2019) in unvaccinated household contacts in the Philippines: A cluster randomised analysis

• Published in: The Journal of infection Vol. 89; no. 4; p. 106260
• Main Authors: Aziz, Asma Binte, Sugimoto, Jonathan Dewing, Hong, Sye Lim, You, Young Ae, Bravo, Lulu, Roa, Camilo, Borja-Tabora, Charissa, Montellano, May Emmeline B., Carlos, Josefina, de Los Reyes, Mari Rose A., Alberto, Edison R., Salvani-Bautista, Milagros, Kim, Hwa Young, Njau, Irene, Clemens, Ralf, Marks, Florian, Tadesse, Birkneh Tilahun
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.10.2024
• Subjects: Adolescent; Adult; Aged; Antibodies, Viral - blood; Child; Child, Preschool; Cluster Analysis; COVID-19 - epidemiology; COVID-19 - prevention & control; COVID-19 Vaccines - administration & dosage; COVID-19 Vaccines - immunology; Double-Blind Method; Family Characteristics; Female; Household contacts; Humans; Indirect effectiveness; Male; Middle Aged; Philippines - epidemiology; Prospective Studies; SARS-CoV-2 - immunology; SCB-2019, SARS-CoV-2 vaccine; Vaccine Efficacy; Vaccines, Subunit; Young Adult; Philippines; Indirect effectiveness; Household contacts; SCB-2019, SARS-CoV-2 vaccine
• ISSN: 0163-4453; 1532-2742; 1532-2742
• DOI: 10.1016/j.jinf.2024.106260

Though observational evidence supports indirect effects of SARS-CoV-2 vaccines, randomised experiments are lacking. To address this gap, the double-blinded, prospective follow-up of the household contacts (HHCs) of Philippine participants of the individually-randomised, placebo-controlled trial of the adjuvanted-subunit protein COVID-19 vaccine, SCB-2019, (EudraCT, 2020–004272–17; ClinicalTrials.gov, NCT04672395) was analyzed in a cluster-randomised fashion. Over an eight-week period, HHCs were followed by rRT-PCR and paired rapid antibody tests (RATs) to detect symptomatic (SCI, primary) and all (ACI, secondary) SARS-CoV-2 infection. A standard analysis estimated the indirect effectiveness of SCB-2019 for each endpoint, excluding HHC RAT-positive at enrollment. A secondary analysis employed enzyme-linked immunosorbent assay (ELISA) results to correct for suspected bias. SCB-2019 (N = 3470) and placebo (N = 3225) exposed HHCs contributed to at least one analysis. The standard analysis estimated that SCB-2019 reduced the risk of SCI by 83% (95% confidence/credible interval [CI: 32% to 96%), with no effect against ACI. The bias-corrected relative risk reduction was 97% (95% CI: 74% to 100%) for SCI and 79% (95% CI: 14% to 96%) for ACI, with an estimated one SARS-CoV-2 infection prevented per 4.8 households where one member received SCB-2019. SCB-2019 demonstrated bias-corrected indirect effectiveness against SARS-CoV-2 infection among HHC, even at a modest coverage level in the household (approximately 25%). Further research into the indirect effects of SARS-CoV-2 vaccines is needed to optimize the impact of limited doses in low and middle-income settings.