The study in which ANSES took part was conducted in collaboration with the UK Health Security Agency (UKHSA), the French company Osivax and the Vaccine Formulation Institute in Switzerland. The results were published in the journal Frontiers in Immunology in June 2023.
Unlike the vaccines currently used against SARS-CoV-2, the tested vaccine is just as effective against the original strain as against the Delta and Omicron variants. One sign of its efficacy on golden hamsters was their weight: there was little weight loss in hamsters that were vaccinated and then infected with one of the variants. On the other hand, their unvaccinated congeners lost 5 to 10% of their body weight after being infected by the original strain or the Delta variant. In addition, the lungs of vaccinated hamsters had significantly fewer lesions, and the rate of virus replication was lower in these animals.
The vaccine's versatility can be explained by its design: it targets the virus's nucleocapsid (N) protein rather than the spike (S) protein, which is present on the virus envelope. The spike protein is more conventionally used to develop a vaccine rapidly but has one drawback: it changes from one variant to the next. "The N protein is conserved between SARS-CoV-2 variants, and more widely within sarbecoviruses, the subgenus containing the coronaviruses responsible for severe acute respiratory syndrome, such as SARS-CoV-1 and SARS-CoV-2," explains Élodie Monchâtre-Leroy, Director of the Nancy Laboratory for Rabies and Wildlife. This protein, present inside the virus, is produced in large quantities when the virus replicates. It is recognised by immune system cells, which enables infected cells to be eliminated and prevents the virus from multiplying.
This conservation of the N protein means that this vaccine can be used beyond the COVID-19 virus: "We want to test it against SARS-CoV-1 to see if it is effective against other coronaviruses responsible for severe acute respiratory syndrome. After SARS-CoV-1 in 2002 and SARS-CoV-2 in 2019, we are not immune to the possibility of another strain emerging in the next few years", explains the scientist. A phase 1 human clinical trial is planned by Osivax for 2024, as well as preclinical trials on other coronavirus strains.
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Primard Charlotte, Monchâtre-Leroy Elodie, Del Campo Judith, Valsesia Séverine, Nikly Elsa, Chevandier Marion, Boué Franck, Servat Alexandre, Wasniewski Marine, Picard-Meyer Evelyne, Courant Thomas, Collin Nicolas, Salguero Francisco J., Le Vert Alexandre, Guyon-Gellin Delphine, Nicolas Florence. OVX033, a nucleocapsid-based vaccine candidate, provides broad-spectrum protection against SARS-CoV-2 variants in a hamster challenge model. Frontiers in Immunology, 14, 2023, doi: 10.3389/fimmu.2023.1188605