Intranasal vaccination provides broad-based protection against respiratory viruses in mice, finds a study pointing that these may also be effective against the new Omicron variant.
The emergence of Covid-19 variants such as Delta and Omicron have sent scientists scrambling to determine whether existing vaccinations and boosters are still effective against new strains of SARS-Cov-2.
The study, published in the journal Science Immunology, showed that nasal vaccines prevented respiratory viruses in mice, while so-called systemic immunisation, which uses an injection to elicit body-wide protection, did not.
Nasal vaccines, but not the shot, also induced antibodies that protected the animals against a variety of flu strains, not just against the strain the vaccine was meant to protect against.
“The best immune defence happens at the gate, guarding against viruses trying to enter,” said Akiko Iwasaki, Professor of Immunobiology at Yale University.
Mucous membranes contain their own immune defence system that combat air- or foodborne pathogens. When challenged, these barrier tissues produce B cells which in turn secrete immunoglobin A (IgA) antibodies. Unlike vaccines which elicit a system-wide immune response, IgA antibodies work locally on mucosal surfaces found in the nose, stomach, and lungs.
While the protective role of IgA-producing cells had been well established in combating intestinal pathogens, Iwasaki’s lab wondered if triggering IgA response might also produce a localised immune response against respiratory viruses.
The team tested a protein-based vaccine designed to jump start an IgA immune response, administering it to mice through injections, and also intranasally.
They then exposed mice to multiple strains of influenza viruses. They found that mice which had received vaccine shot intranasally were much better protected against the respiratory influenza than those that received injections.
While both vaccine injections and nasal vaccines increased levels of antibodies in the blood of mice, only the nasal vaccine enabled IgA secretion into the lungs, where respiratory viruses need to lodge to infect the host, Iwasaki said.
If the nasal vaccines prove to be safe and efficient in humans, Iwasaki envisions them being used in conjunction with current vaccines and boosters that work system wide in order to add immune system reinforcements at the source of infection.