Impact of vaccination with SCB-2019 COVID-19 vaccine on transmission of SARS-CoV-2 infection: a household contact study in the Philippines

Background An exploratory household transmission study was nested in SPECTRA, the phase 2/3 efficacy study of the adjuvanted recombinant protein-based COVID-19 vaccine SCB-2019. We compared occurrence of confirmed COVID-19 infections between households and household contacts of infected SPECTRA participants who were either placebo or SCB-2019 recipients. Methods SPECTRA trial participants at eight study sites in the Philippines who developed rRT-PCR-confirmed COVID-19 were contacted by a study team blinded to assignment of index cases to vaccine or placebo groups to enroll in this household transmission study. Enrolled households and household contacts were monitored for three weeks using rRT-PCR and rapid antigen testing to detect new COVID-19 infections. Results Observation of the households of 154 eligible COVID-19 index cases, 130 symptomatic and 24 asymptomatic at diagnosis, revealed household secondary attack rates for any COVID-19 infection of SCB-2019 index cases of 0.76% (90% CI: 0.15–3.90) compared with 5.88% (90% CI: 3.20–10.8) in placebo index case households, a relative risk reduction of 79% (90% CI: -28–97). The relative risk reduction of symptomatic COVID-19 was 84% (90% CI: 28–97) for household contacts of all COVID-19 infected index cases, and 80% (90% CI: 7–96) for household contacts of index cases with symptomatic COVID-19. Conclusions In this prospective household contact study vaccination with SCB-2019 reduced SARS-CoV-2 transmission in households, so decreasing infections of household contacts, compared with placebo. ### Competing Interest Statement P.L. and J.G. are full-time employees of the study sponsor. Other authors declare they have no conflicts. ### Funding Statement This work was supported by the Coalition for Epidemic Preparedness Innovations (Grants RRCL 2001 and RCL2202) and Clover Biopharmaceuticals. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The protocol was approved by the Single Joint Research Ethics Board (SJREB), the respective Institutional Review Boards (IRB) of the eight study sites and the International Vaccine Institute IRB I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present work are contained in the manuscript