Clinical Trial Info

A Study Looking at the Effectiveness and Safety of a COVID-19 Vaccine in South African Adults

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This is a study to evaluate the effectiveness and safety of a coronavirus disease 2019 (COVID-19) vaccine called SARS-CoV-2 rS with Matrix-M1 adjuvant in a minimum of approximately 2,960 to a maximum of approximately 4,164 healthy HIV-negative (HIV-) adult participants and in approximately 240 medically stable HIV-positive (HIV+) adult participants in up to 15 sites across South Africa.

A vaccine causes the body to have an immune response that may help prevent the infection or reduce the severity of symptoms. An adjuvant is something that can make a vaccine work better. This study will look at the protective effect, body's immune response, and safety of SARS-CoV-2 rS with Matrix-M1 adjuvant in these study populations.

Approximately 4,400 participants in the study will randomly be assigned to receive SARS-CoV-2 rS with Matrix-M1 adjuvant or placebo. Each participant in the study will receive a total of 2 intramuscular injections over the course of the study.

Interim Results

On May 5, 2021, The New England Journal of Medicine published interim results.

Of 6324 participants who underwent screening, 4387 received at least one injection of vaccine or placebo.

Approximately 30% of the participants were seropositive for SARS-CoV-2 at baseline. Among 2684 baseline seronegative participants (94% HIV-negative and 6% HIV-positive), predominantly mild-to-moderate Covid-19 developed in 15 participants in the vaccine group and in 29 in the placebo group (vaccine efficacy, 49.4%; 95% confidence interval [CI], 6.1 to 72.8).

Vaccine efficacy among HIV-negative participants was 60.1% (95% CI, 19.9 to 80.1). Of 41 sequenced isolates, 38 (92.7%) were the B.1.351 variant. Post hoc vaccine efficacy against B.1.351 was 51.0% (95% CI, −0.6 to 76.2) among the HIV-negative participants. Preliminary local and systemic reactogenicity events were more common in the vaccine group; serious adverse events were rare in both groups.


The NVX-CoV2373 vaccine was efficacious in preventing Covid-19, with higher vaccine efficacy observed among HIV-negative participants. Most infections were caused by the B.1.351 variant. (Funded by Novavax and the Bill and Melinda Gates Foundation)