In a recent study published in the New England Journal of Medicine, scientists have summarized the safety and efficacy profile of the full-length spike-based coronavirus disease 2019 (COVID-19) vaccine NVX-CoV2373 (Novavax). The findings reveal that the two-dose regimen of the vaccine is almost 90% effective against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Moreover, the vaccine shows high efficacy against the B.1.1.7 variant (Alpha) of SARS-CoV-2.
The NVX-CoV2373 (Novavax) is a Matrix-M-adjuvanted COVID-19 vaccine that contains a recombinant nanoparticle full-length spike protein of SARS-CoV-2 (5 µg) as immunogen. For full immunization, two doses of the vaccine are administered intramuscularly at an interval of 21 days. In earlier clinical trials, the vaccine has shown acceptable safety and immunogenic profiles in healthy adult volunteers.
In the current phase 3, randomized, placebo-controlled clinical trial, the scientists have assessed the safety and efficacy profiles of NVX-CoV2373 in preventing symptomatic COVID-19 among adult volunteers aged 18 to 84 years. All participants were seronegative at the baseline during recruitment. The trial was conducted in 33 locations in the United Kingdom when the B.1.1.7 variant was predominantly circulating.
A total of 15,187 men and non-pregnant women volunteers were enrolled for the trial. They were either healthy or had chronic medical conditions, including HIV infection, cardiorespiratory, renal, hepatic, or neurological diseases, or obesity. Individuals with a history of documented COVID-19 or those undergoing immunosuppressive therapy were excluded from the trial.
The volunteers were randomized into two groups, with one group receiving two vaccine doses 21 days apart (vaccine group) and the other group receiving normal saline (placebo group).
The trial's primary outcome was vaccine efficacy against the first manifestation of medically confirmed mild, moderate, or severe COVID-19 at least 7 days after receiving the 2nd vaccine dose.
The safety and efficacy profiles of vaccinated and placebo-treated volunteers were assessed in the trial.
For the safety analysis, a total of 2,310 volunteers were included. After the 1st and 2nd vaccine/placebo doses, a significantly higher number of volunteers in the vaccine group reported local adverse events than that in the placebo group.
The most common local adverse event among vaccinated volunteers was pain or tenderness at the injection site. However, the event was short-term and mild to moderate in severity.
Similarly, systemic adverse events were reported more frequently by vaccinated volunteers than placebo-treated volunteers. The most commonly reported systemic adverse events were headache, muscle pain, and fatigue both after the 1st and 2nd vaccine doses. These events were also short-term and mild to moderate in severity. Only two volunteers reported high-grade fever (>40°C).
Younger vaccinated volunteers reported systemic and local adverse events more frequently than their elder counterparts.
The frequency of unsolicited adverse events was higher among vaccinated volunteers than placebo-treated volunteers. In one volunteer, viral myocarditis occurred three days after the 2nd vaccine dose. However, the person achieved complete recovery after two days of hospitalization. No anaphylactic reaction or vaccine-related induction in COVID-19 risk were observed among volunteers.
During the trial period, one person in the vaccine group and one person in the placebo group died due to COVID-19. In the vaccine group, death occurred in a person who developed COVID-19 symptoms seven days after receiving the 1st vaccine dose.
Among 14,039 volunteers, 10 in the vaccine group and 96 in the placebo group developed mild, moderate, or severe COVID-19 at least seven days after 2nd dose. Based on these observations, the vaccine efficacy was estimated to be 89.7%.
The incidence of severe COVID-19 occurred only among placebo-treated volunteers. No COVID-19 related hospitalization or death occurred among vaccinated volunteers. Among ten volunteers who were 65 years of age or older and eventually developed COVID-19, one was from the vaccine group, and nine were from the placebo group.
For further efficacy analysis, the volunteers were sub-divided according to age, race, and presence of comorbidities. The findings revealed that the vaccine efficacy was 88.9% among volunteers aged 65 years or above. Moreover, a comparable vaccine efficacy of about 90% was observed among volunteers with or without comorbidities.
After 14 days of administering 1st dose, the vaccine efficacy was estimated to be 83.4%. Because of the significantly lower number of non-White volunteers, conclusive assessments could not be made regarding vaccine efficacy among different races or ethnic groups.
Regarding emerging viral variants, the vaccine was found to be 86.3% and 96.4% effective against the B.1.1.7 and non-B.1.1.7 variants, respectively.
Overall, the trial findings clearly indicate that the NVX-CoV2373 vaccine effectively prevents infections by SARS-CoV-2 and its variants. Moreover, the vaccine exhibits an acceptable safety profile.