On Jun. 1, 2021, the National Institutes of Health announced that it had started a Phase 1/2 clinical trial in which adult volunteers who had been fully vaccinated against COVID-19 received booster doses of different COVID-19 vaccines to determine the safety and immunogenicity of mixed boosted regimens.

The National Institute of Allergy and Infectious Diseaseswas leading and funding the study through the Infectious Diseases Clinical Research Consortium, a clinical trials network that encompasses the Instituteﾒs long-standing Vaccine and Treatment Evaluation Units.