Johannesburg, May 7 : A Covid-19 vaccine developed by the US-based biotechnology company Novavax has been found effective against Coronavirus' B1351 variant, first identified in South Africa, results of a trial have shown. The Phase 2b randomised, observer-blinded, placebo-controlled trial conducted in South Africa evaluated efficacy, safety and immunogenicity in healthy adults, and in a small cohort of medically stable adults living with human immunodeficiency virus (HIV). The Novavax vaccine demonstrated an overall efficacy of 49 per cent in the initial analysis. Among healthy adults without HIV, the Novavax vaccine demonstrated efficacy of 60 per cent in the initial analysis, and 55 per cent in the subsequent complete analysis.AA The initial analysis, published in New England Journal of Medicine, suggested that prior infection with the original Covid-19 strain did not protect against subsequent infection by the variant predominantly circulating in South Africa through 60 days of follow-up. However, with additional follow-up, the trial indicates that there may be a modest protective effect of prior exposure with the original Covid-19 strain. Among placebo recipients, at 90 days of follow-up, the illness rate was 8.0 per cent in baseline seronegative participants and 5.9 per cent in baseline seropositive participants. "The data make a compelling case for use of the Novavax Covid-19 vaccine in settings where the B1351 variant dominates -- which is most of southern Africa -- to reduce the risk of mild disease and also to maximise the opportunity for protection against severe Covid," said Shabir Madhi, Professor and Dean of the Faculty of Health Sciences at the University of the Witwatersrand, Johannesburg (Wits), South Africa. "Further work is required for Novavax and all other Covid-19 vaccines, particularly in people living with HIV," Madhi added. NVX-CoV2373 is a protein-based vaccine candidate engineered from the genetic sequence of the first strain of SARS-CoV-2, the virus that causes Covid-19 disease. The company is also expected to apply for US authorisation in the next few weeks. /IANS