In a recent study published in JAMA Network Open, researchers discuss the efficacy of a primary cycle of the protein recombinant coronavirus disease 2019 (COVID-19) vaccine Novavax (NVX-CoV2373) in protecting against symptomatic COVID-19 and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection.

Study: Estimated Effectiveness of a Primary Cycle of Protein Recombinant Vaccine NVX-CoV2373 Against COVID-19. Image Credit: Vladimka production / Shutterstock.com

Background

The high morbidity and mortality rates during the COVID-19 pandemic led to herculean efforts to rapidly develop vaccines against SARS-CoV-2. These efforts culminated in the development of adenoviral vector, inactivated viral, protein recombinant, and messenger ribonucleic acid (mRNA) vaccines.

A considerable percentage of the European population completed their primary vaccination against COVID-19 by the end of 2022. In Italy, most of the population had completed their primary vaccination series with mRNA vaccines.

Despite widespread vaccine coverage, the emergence of novel viral variants capable of evading vaccine- or infection-induced immunity, combined with the natural waning of vaccine-induced immunity, resulted in the persistence of SARS-CoV-2 among humans. Given the rapid pace at which SARS-CoV-2 is evolving and new Omicron subvariants are emerging, it is important to estimate the efficacy of alternate vaccines in preventing infections.

About the study

In the present study, researchers used general population data on administered vaccinations and vaccine-related demographic and clinical information from Italy’s vaccine registry. These data were used to evaluate the efficacy of NVX-CoV2373 in preventing symptomatic COVID-19 and SARS-CoV-2 infection during Omicron-dominant periods.

The study used data on COVID-19 outcomes and SARS-CoV-2 infections confirmed through antigen testing or polymerase chain reaction (PCR) assay obtained from the National Integrated Surveillance System. The study population consisted of a retrospective cohort of all adults who completed their primary vaccination cycle with the protein recombinant vaccine NVX-CoV2373 between February and September 2022.

A minimum follow-up period of three weeks was ensured for each participant. The dominant Omicron sub-lineages circulating during the study period were BA.2 and BA.5. Individuals with a history of SARS-CoV-2 infection or those who had completed the primary vaccination regimen using any other vaccine were excluded from the study.

The examined outcomes were the incidence or risk of symptomatic COVID-19 and PCR or antigen test-confirmed SARS-CoV-2 infection. The risk of infection or symptomatic disease was evaluated at various stages, including after partial and complete vaccination.

The partial vaccination period began 15 days after the administration of the first dose and ended two weeks after the administration of the second dose based on the assumption that protection from infection in the first two weeks after the first vaccination was similar to that when unvaccinated. Similarly, the complete vaccination stage began 15 days after administering the second and final primary vaccination dose.

Incidence rate ratios of both primary outcome measures were calculated. All analyses were adjusted for major confounding factors, including age, sex, and area of residence.

Study findings

The protein recombinant vaccine NVX-CoV2373 was effective in protecting against symptomatic COVID-19 and SARS-CoV-2 infection when the Omicron variant and its subvariants were the dominant circulating strains.

The estimated effectiveness of NVX-CoV2373 in protecting against SARS-CoV-2 infection decreased from 41% to 28% in the four months following the completion of the primary vaccination cycle. The efficacy of the primary vaccination cycle was comparatively higher at 50% in protecting against symptomatic infection.

Early clinical trials for NVX-CoV2373 reported 95% vaccine efficacy against the ancestral SARS-CoV-2 variant and 85% efficacy against the SARS-CoV-2 Alpha variant. These vaccine efficacy rates were comparable to the reported efficacy for mRNA vaccines against the same variants.

One of the limitations of the current study was the small section of the population that opted for the protein recombinant vaccine, as vaccine efficacy in protecting against hospitalization or mortality could not be assessed. The small sample size also prevented stratification of the results by age.

The study population also consisted of individuals younger than 80 with no significant comorbidities, making the results non-generalizable for the larger population.

Conclusions

The study findings suggest that the NVX-CoV2373 vaccine was effective in lowering the risk of SARS-CoV-2 infections and symptomatic COVID-19. The efficacy in protecting against SARS-CoV-2 infection decreased in the four months following the completion of the primary vaccination round; however, protection against symptomatic COVID-19 remained stable.

Since NVX-CoV2373 has recently been approved as a booster vaccine, the efficacy of its booster doses remains to be evaluated.

Written by

Dr. Chinta Sidharthan

Chinta Sidharthan is a writer based in Bangalore, India. Her academic background is in evolutionary biology and genetics, and she has extensive experience in scientific research, teaching, science writing, and herpetology. Chinta holds a Ph.D. in evolutionary biology from the Indian Institute of Science and is passionate about science education, writing, animals, wildlife, and conservation. For her doctoral research, she explored the origins and diversification of blindsnakes in India, as a part of which she did extensive fieldwork in the jungles of southern India. She has received the Canadian Governor General’s bronze medal and Bangalore University gold medal for academic excellence and published her research in high-impact journals.