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Dr Gérald Kierzek (Medical Director of Doctissimo)
When we talk about vaccines, we immediately think of an injection. Scientists are, however, trying to develop other routes for vaccination, notably nasal. Could it be a way to stop contamination between individuals? What about Covid-19? The point of view of Dr Kierzek, emergency doctor and medical director of Doctissimo.
Vaccines against Covid-19 have been developed to protect the population, in particular against severe forms, but they do not prevent the transmission of the virus. Could a nasally administered vaccine be more effective against viral transmission?
Work on mucosal vaccination
By injecting a vaccine through the nose, immune cells in the mucous membranes of the respiratory system would be better able to recognize and block the virus as soon as it enters the body. According to the work of a team of CNRS researchers, in association with Inserm and the universities of Nantes and Angers, a mucosal vaccine that they have developed is “capable of ensuring the total survival of a group of mice infected with a version of the virus adapted to this species, while it decimates 100% of unvaccinated mice”. However, its effects on viral transmission have not been studied by researchers.
More IgA than IgG
One of the other advantages of a nasal vaccination is that it induces more type A immunoglobulins than type G by the immune cells present in the nose. The IgAs”capture“more viruses than IgGs and are also more versatile. This would prevent even moderate forms of the disease, and subsequently block transmission between individuals.” This is the interest of this type of vaccines explains Dr Gérald Kierzek. “They can stop transmission but do we really need to vaccinate everyone? Because natural immunity is important and also effective. It should rather be seen as a complementary approach, in my opinion“.
Two candidate vaccines for Covid-19
Regarding Covid-19, two vaccine candidates have been announced by China and India. The first, made in China by CanSino Biologics is a candidate vaccine based on a recombinant adenovirus expressing the Spike protein. Administered orally using a nebulizer, it is not really a nasal vaccine, but it still passes through the respiratory tract, therefore the mucous membrane. It was still approved by China as a booster dose against Covid-19.
The second was developed by the company Bharat Biotech. Called incovacc, it is a vaccine that is used in two doses, administered through the nose. Like the first, this vaccine also uses a modified, attenuated adenovirus to deliver the Spike protein from SARS-CoV-2. Currently in the preclinical stage, this vaccine candidate has shown results in chimpanzees, but nevertheless presents risks of bronchial inflammation. Finally, remember that, for the time being, neither country has published the results of human clinical studies supporting their decision to approve these vaccines.
Research to develop a nasal vaccine continues
International research around a vaccine in the form of a nasal spray continues. Thus, AstraZeneca announces disappointing results for its first clinical trials of its candidate nasal vaccine. As for the Inrae researchers (BioMAP laboratory, Joint University-INRAE ISP 1282 research unit), they announce that they want to move on to clinical trials in humans for their candidate vaccine in 2023. There remains the question of its administration, with the spray suitable which will allow its diffusion only in contact with the mucous membrane of the nose, in order to avoid any risk of excessive immune reaction.