U.S. drug developer Novavax Inc said on Monday that it is starting a mid-stage study of its experimental COVID-19 vaccine in South Africa, as the country experiences a surge in coronavirus cases. The Phase 2b trial study of NVX-CoV2373 will be conducted on about 2,665 healthy adults and will evaluate the safety and immunogenicity in about 240 medically stable, HIV-positive adults, the company said in a statement. "Because South Africa is experiencing a winter surge of COVID-19 disease, this important Phase 2b clinical trial has the potential to provide an early indication of efficacy, along with additional safety and immunogenicity…