Study design and participants
DISEASE
This multicentre, randomised, double-blind, placebo-controlled, case-driven, and adaptive design phase 3 trial was done at 33 sites (private or public hospitals, clinical research centres, or Center for Disease Control and Prevention) in Colombia, the Philippines, South Africa, and Viet Nam (Participants in South Africa and Viet Nam were limited to those who had previously received one or more doses of SARS-CoV-2 vaccines due to the requirements of national regulatory authorities. On March, 2022, an addendum was added to the protocol (version 2.0, dated Aug 10, 2021) to include individuals in Viet Nam who had received the last vaccine dose 3–6 months before signing the informed consent, because a nationwide mass booster SARS-CoV-2 vaccination campaign was being carried out.The trial protocol, the written informed consent form, and other materials related to the participants were approved by the ethics committees at all sites. The trial was done in accordance with the Declaration of Helsinki and the Good Clinical Practice guidelines. The study protocol is available in the 