The NVX-CoV2373 nanoparticle vaccine was found to be effective in preventing COVID-19, according to authors of a 2019nCoV-501 Study Group multicenter trial published in the New England Journal of Medicine.

In this phase 2a-b study in South Africa ( Identifier: NCT04533399), HIV-negative adults or medically stable HIV-positive adults (mean age of all participants, 32 years) were randomly assigned in a 1:1 ratio to receive 2 intramuscular injections 21 days apart of either saline placebo or the NVX-CoV2373 vaccine, each dose of which contained 5 μg of recombinant spike protein with 50 μg of Matrix-M1 adjuvant. A total of 6324 participants underwent screening and 4387 received at least one injection of vaccine (n=2199) or placebo (n=2188).

The study’s primary end points were safety and efficacy of the vaccine against laboratory-confirmed symptomatic COVID-19 at least 7 days after the second dose among participants without previous SARS-CoV-2 infection.

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At baseline approximately 30% of participants tested positive for SARS-CoV-2. Of the 2684 participants who tested seronegative at baseline, 94% were HIV-negative and 6% were HIV-positive. By day 28, mild to moderate COVID-19 was observed in 15 participants from the vaccine group and 29 from the placebo group (vaccine efficacy, 49.4%; 95% CI, 6.1-72.8). Efficacy was 60.1% (95% CI, 19.9–80.1) among HIV-negative participants. The study was not powered to determine vaccine efficacy in the small number of HIV-positive participants. Among HIV-positive and SARS-CoV-2 negative participants at baseline, 4 of 76 participants in the vaccine group and 2 of 72 participants in the placebo group developed COVID-19.

Whole-genome sequencing of 41 suitable isolates found 38 (92.7%) were the B.1.351 variant. A post-hoc analysis of NVX-CoV2373 efficacy against this variant in HIV-negative participants was 51.0% (95% CI, -0.6 to 76.2). Serious adverse events were rare in both the placebo and vaccine groups. Preliminary local and systemic reactogenicity events were more common in the vaccine group.

The investigators noted several study limitations. The efficacy results are preliminary, with median follow-up times of 66 days and 45 days after the first and second doses, respectively, and are limited to the primary end point and subgroups of the primary end point, as well as the post hoc analysis of B.1.351 variant sequencing data.

“We have found that a prototype-sequenced NVX-CoV2373 vaccine was efficacious and induced notable cross-protection during a pandemic with a dominant circulation of the B.1.351 variant,” the investigators concluded.


Shinde V, Bhikha S, Hoosain Z, et al. Efficacy of NVX-CoV2373 Covid-19 vaccine against the B.1.351 variant. N Engl J Med. Published online May 5, 2021. doi:10.1056/NEJMoa2103055