Novavax a biotechnology company developing next-generation vaccines for serious infectious diseases, announced preliminary data demonstrating that a single booster dose of its recombinant nanoparticle protein-based COVID-19 vaccine with Matrix-M adjuvant, NVX-CoV2373, given six months after an initial two-dose regimen, elicited a 4.6-fold increase in functional antibody titers. Additionally, functional ACE-2 binding inhibition antibodies cross-reactive with the Delta (B.1.617.2) variant were more than 6-fold higher than the primary vaccination series. Complete data from the study will be submitted to a peer-review publication and posted to a preprint server.

The results come from an ongoing Phase 2 study in the U.S. and Australia in which select participants in the 5-microgram dose cohort received a 5-microgram booster dose 189 days after the initial two-dose regimen to examine the functional immune response.

"The strong results from this study reinforce our confidence in the potential for a booster dose of NVX-CoV2373 to provide broad protection against disease, including from known and emerging variants," said Gregory M. Glenn, M.D., President of Research and Development, Novavax. "Given the evidence that natural and vaccine-induced immunity wanes over time, the continuation of our proactive clinical development program will be critical to understanding and demonstrating the effectiveness of our recombinant nanoparticle COVID-19 vaccine."

Twenty-eight days following boosting, anti-spike IgG increased approximately 4.6-fold compared to the peak response seen after the second dose (Day 217 GMEU = 200,408 (95% CI: 159,796; 251,342)). This boosted value represents a 3.7 to 4.4-fold increase in anti-spike IgG values that were associated with protection in Novavax' PREVENT-19 and U.K. Phase 3 clinical studies.

Similarly, wild-type neutralization responses increased approximately 4.3-fold compared to the peak response seen after Dose 2 (IC50 neutralization titers = 6,231 (95% CI: 4,738; 8,195)). This boosted value represents a 4.6 to 5.5-fold increase over the neutralization response associated with protection in the PREVENT-19 and U.K. Phase 3 clinical trials. Older participants (aged 60-84) showed a 5.4-fold increase in antibody responses, while younger participants (aged 18-59) showed a 3.7-fold increase. Very high levels of functional antibodies to the Alpha (B.1.1.7), Beta (B.1.351) and Delta variants were induced by boosting with NVX-CoV2373, with a 6.6-fold higher Delta variant-specific response when compared to the Delta response observed with the primary vaccination series.

The administration of the booster dose was generally well-tolerated. Local and systemic reactogenicity increased between Dose 1, Dose 2 and Dose 3, with 90% of symptoms rated as mild or moderate after the third dose.

In addition to the ongoing Phase 1/2 boost study, NVX-CoV2373 is one of seven COVID-19 vaccines being evaluated as part of COV-Boost, a "mix-and-match" study being conducted by the University Hospital Southampton NHS Foundation Trust and the other U.K. National Institute for Health Research sites and supported by the U.K. Vaccines Task Force and Department of Health and Social Care. COV-Boost is evaluating heterologous boosting in individuals who previously received two doses of an authorized vaccine. NVX-CoV2372 is also being evaluated in Com-COV2, which is exploring the heterologous regimen of COVID-19 vaccines from different manufacturers.