Efficacy of the Novavax Vaccine Against COVID-19: Nanoparticle Technology to the Test

In healthy adults, two doses of the NVX-CoV2373 (Novavax) vaccine has an efficacy of almost 90% against SARS-CoV-2 infection in all severity types. Furthermore, it has proven to be effective against the alpha variant (B.1.1.7).

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The Novavax vaccine is a recombinant nanoparticle containing full-length spike glycoprotein. It had already been shown to be safe and to generate a robust immune response in healthy adults, but data on its efficacy, immunogenicity, and safety in a larger population were lacking.

This phase 3 study included participants between 18 and 34 years old, from 33 sites in the United Kingdom, who were randomized 1:1 to receive two intramuscular 5-µg doses of Novavax vs. placebo administered 21 days apart. 

The primary efficacy endpoint was virologically confirmed mild, moderate, or severe infection with an onset at least 7 days after the second injection. All participants were serologically negative at randomization.

Over 15,000 participants were randomized; almost 30% were aged >65 years old and about half had preexisting conditions.

A week after the second dose, 10 participants from the vaccine arm vs. 96 in the placebo arm presented symptoms onset. This means efficacy is 89.7% (95% confidence interval: 80.2 to 94.6).

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None of the 10 participants who tested positive in the vaccine group required hospitalization or died.

Five participants had severe disease, all in the placebo group.

Further analysis showed an efficacy of 86.3% for the B.1.1.7 variant (alpha variant), and 96.4% for the rest of the participants.

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Adverse events were mostly mild and transient; severe adverse events were rare and similar in both arms.

In other words, this new vaccine presents excellent results that reinforce the current offering.


Two doses of Novavax provide an 89.7% efficacy against COVID-19 in all severity types. Additionally, it is highly efficient against the alpha variant.

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Original Title: Safety and Efficacy of NVX-CoV2373 Covid-19 Vaccine.

Reference: P.T. Heath et al. NEJM 2021. DOI: 10.1056/NEJMoa2107659.

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