The vaccine, developed with the biotech company TheraVectys, is based on the use of a lentiviral vector. The vector, stripped of all viral genes so that it is harmless for humans, is used to produce the spike protein. This protein, which forms spikes all around the virus, is the entry key allowing the virus into cells. The aim is to induce a specific immune response to the protein, triggering the production of both antibodies capable of recognizing the SARS-CoV-2 virus and cytotoxic cells capable of destroying infected cells and thereby preventing infection from developing.
Administration by nasal spray is believed to be the most effective means of delivering the vaccine. An effective coronavirus vaccine should induce vaccine protection at the site where the virus enters the body, namely the respiratory tract. It is thought that neutralizing antibodies present in the blood actually only contribute minimally to protection. This vaccine candidate drastically reduces lung viral loads (by a factor of 100,000). While vaccines generally induce production of IgG antibodies, administration by nasal spray induces increased production of IgA in the lung mucosa, which seems to offer much better protection against infection.
This type of vector has proved to be promising against other viruses. A therapeutic vaccine for HIV obtained good safety results in Phase I in humans. Therapeutic vaccines are also under development – currently in the preclinical phase – for various types of cancer, with encouraging results.