JULIE STEENHUYSEN NOVAVAX Inc's COVID-19 vaccine had efficacy of 51% against infections caused by the South African variant among people who were HIV negative, and 43% in a group that included people who were HIV positive, according to a new analysis published on Wednesday. The variant, known as B.1.351, carries mutations that threaten the efficacy of COVID-19 vaccines, several studies have shown. Most vaccine makers, including Novavax, are testing versions of their vaccines to protect against emerging variants. The Novavax post-hoc analysis was published in the New England Journal of Medicine along with full data from the company's trial in…