Skip to main content

Evaluation of a SARS-CoV-2 Vaccine NVX-CoV2373 in Younger and Older Adults

Our take —

Vaccines using the nanoparticle/Matrix-M1 adjuvant approach, like NVX-CoV2373 (Novavax), have been widely studied and have a very acceptable safety profile. This phase 2 trial report, available as a preprint and thus not yet peer-reveiwed, found that both the 5ug and 25ug doses of NVX-CoV2373 were effective at inducing production of IgG and neutralizing antibodies, while the 25ug dose had a higher incidence of local reactogenicity in both younger and older adults. Therefore, Novavax will move forward with a 2-dose regimen of 5ug NVX-CoV2373 administered 21 days apart in phase 3 trials. Trials are currently ongoing in South Africa, the UK, the US, and Mexico.

Study design

Randomized Controlled Trial

Study population and setting

This paper described the phase 2 trial of the Novavax vaccine, NVX-CoV2373, which is composed of trimeric full-length SARS-CoV-2 spike proteins and adjuvant. The trial took place between August 24 and September 25, 2020. 1283 participants in two age groups were studied: younger (18-59 years) and older (60-84 years) adults, at nine sites in Australia and eight sites in the US. Participants received either one or two doses of 5ug or 25ug NVX-CoV2373 or placebo 21 days apart. Immunogenicity and safety data were studied through day 35, including adverse events, reactogenicity within 7 days of receiving the vaccine, IgG response, and neutralizing antibody production.

Summary of Main Findings

The most commonly reported local adverse events were pain and tenderness at the injection site, while the most common systemic adverse events were muscle pain, fatigue, headache, and malaise. Fever was only reported in less than 2% of all participants. Reactogenicity occurred at higher frequency in younger participants compared to older participants, and the systemic reactions were also more common after the second dose. Seroconversion rates of IgG production were 99% and 100% (younger participants) and 97% and 99% (older participants) after 2 doses of 5ug or 25ug, respectively. Additionally, seroconversion of neutralizing antibodies were 100% and 100% (younger participants) and 100% and 96% (older participants) after 2 doses of 5ug or 25ug, respectively. Higher amounts of neutralizing antibodies were detected in both younger and older participants compared to convalescent sera.

Study Strengths

This vaccine uses a recombinant protein approach, which is different than the other already approved COVID-19 vaccines, making it novel. This trial studied multiple doses and dosing regimens for NVX-CoV2373, and also included both younger and older adults.


The study included 87% white participants. Future trials for NVX-CoV2373 included a more diverse population in South Africa and Mexico, but these data are not reported here. No analysis of T-cells was included here, only study of antibodies, even though no true correlate of vaccine protection has been defined. Finally, data was only published here for observations through day 35, so no-long term data is provided yet.

Value added

First report of phase 2 results from the Novavax NVX-CoV2373 vaccine, with results in both younger and older adults

This review was posted on: 12 March 2021