Researchers at the University of Basel have developed a live nasal drop vaccine for Covid-19 that prevents infection and transmission of the virus. The vaccine is designed to draw the line of defence against the Sars-CoV-2 virus in the nasal mucosa, rather than in the blood like traditional injected inactivated vaccines. The single-cycle live vaccine uses modified corona viruses that can penetrate the mucous membrane but cannot multiply there. Two genetic interventions in their genome ensure that these viruses do not cause infection. In trials with hamsters, none of the vaccinated animals became ill, even after subsequent exposure to a high dose of wild-type virus.
The vaccine could offer protection against new Sars-CoV-2 variants, as the immune system is exposed to many much less changeable components than just the spike protein. The researchers have applied for a patent for their method and are working with the Swiss start-up RocketVax to bring the vaccine into the first clinical test phase. The Swiss Federal Office of Public Health has approved the safety of the method. The vaccine candidate also proved to be quite stable and can be stored at refrigerator temperatures.
Unlike traditional vaccines that prevent disease but not infection, the Basel vaccine appears to offer sterile immunity against Covid-19.
In addition, the researchers are working on using the new vaccination strategy against other viral diseases, such as the dengue and chikungunya viruses, which are transmitted by tiger mosquitoes that are now present in many countries.
Compared to other live vaccine candidates, the developers of the Basel vaccine went a step further in weakening the virus so that the virus can no longer multiply at all. This was achieved by a targeted removal of entire genes, rather than by chance mutations during cultivation.
In a separate development, scientists from the Berlin Charité, the Freie Universität Berlin, and the Max Delbrück Center for Molecular Medicine in Berlin are working on a nasal spray live vaccine candidate using a slightly more sophisticated method of codon de-optimisation. In trials with hamsters, this vaccine candidate elicited stronger mucosal immunity than compared injected inactivated vaccines. Double immunisation with the nasal spray vaccine produced the best protection. The researchers are currently preparing a first clinical study with humans, with RocketVax also involved.
