Would a vaccine injected directly into the nostrils be more effective in preventing coronavirus infection? This is indicated by a Swedish study published September 14, 2022 in the New England Journal of Medicine, which shows that people with a certain type of anti-Covid antibody in their nose are less at risk of infection than people with antibodies in their blood but not in their nose.
IgA antibodies in the nose close the door to intruders
All currently tested Covid-19 vaccines are administered intramuscularly in the arm. Once injected, they will stimulate the immune system to produce antibodies against the coronavirus spike protein, specifically immunoglobulin G (IgG). But most of these antibodies will be found in the blood of the vaccinated person. However, the virus first infects the upper respiratory tract, the entry point of the coronavirus into our bodies. In particular, Omicron and its sub-variants, which partially avoid these antibodies (immunity acquired after vaccination or previous infection) as well as our innate immunity and thus infect us. Unless one type of these antibodies (immunoglobulins A or IgA) is in force right at that door!
Researchers at the Karolinska Institute in Sweden identified this increased protection by examining the antibodies of 338 caregivers who received three doses of the vaccine, 57 of whom became infected with Omicron after vaccination. Almost all of the people analyzed (337 people) had IgG against Covid in their nasal mucosa, but only 62% of them also had IgA against the virus there. However, people with high levels of these IgA in the nostrils had a significantly lower risk of infection. This protection worked even if these antibodies were specific to the original coronavirus strain, but they were more effective if they were specific to the BA.1 Omicron variant.
Nasal vaccines mimic the immune response to infection.
These nostril mucosal IgA levels did not correlate with mucosal or blood IgG levels. It also did not depend on the type of vaccine or the time elapsed since the third dose. The age or gender of the individual was also not associated with the presence or absence of these immunoglobulins in the nose. The only relationship shown was with prior infection, which had higher levels of IgA (but not IgG). Probably because an infection that starts in the nose triggers a local immune response in that area.
“It is tempting to think that a vaccine given through the nose or mouth when SARS-CoV-2 enters the body could elicit a local immune response that could prevent early infection,” suggests Charlotte Tali, author of the study. study in reported. Thus, the idea is to mimic the local reaction in the nostrils after infection while avoiding the negative effects of the infection. An opportunity that several vaccines in development want to exploit. This is, for example, the case vaccine candidate developed by the BioMAP team from INRAE-University of Tours. Belonging preclinical studies in mice, this nasal vaccine is expected to prevent infection well (at least for the Delta variant, not yet known for the Omicron variant). Just like the vaccine candidate developed in Germany by a group of researchers from the Free University (FU) Berlin, successfully tested on hamsters. However, human clinical trials are still needed to confirm whether such increased protection will exist in our species. However, another nasal vaccine has just been validated in China, so we should have data on the real effectiveness of this approach soon.