Nasal vaccines can induce broader viral protection than injections

Compelling new preclinical research from scientists at Yale University has found that intranasal vaccination may be much more effective at generating immunity against a number of respiratory viruses compared to more conventional injection vaccination.

The COVID-19 pandemic has rekindled great interest in administering vaccines by inhalable nasal spray. Not only is this type of vaccine delivery system much easier to administer, but for several years researchers have speculated that it would potentially be more effective against infections that initially take hold in the upper respiratory tract. .

“The best immune defense occurs at the door, protecting against viruses trying to enter,” says lead author of the new study, Akiko Iwasaki.

Immunoglobulin A (IgA) antibodies are one of the first line soldiers of the immune system. These antibodies are mainly secreted by the mucous surfaces of the body, mainly seen in the nose, intestines and lungs.

The idea behind a nasal vaccine is that it could directly train the mucous membranes of the nose to target certain airborne pathogens so that an immune response can be triggered as soon as a virus enters the human body. This new study shows promise that nasal vaccines not only induce effective IgA responses, but can also promote broad immunity against more than one viral strain in a vaccine.

The study reports on a series of experiments in mice comparing the effects of an influenza vaccine given intranasally and more traditionally by injection. The researchers exposed the mice to a number of different flu strains beyond the one the vaccine was supposed to target. The results revealed that animals receiving the nasal vaccine were significantly better protected against a wide variety of influenza strains compared to mice receiving injections.

Focusing on IgA responses, the researchers found that not only did the nasal vaccine induce IgA responses in the nasal mucosa, but that significant levels of IgA secretion were also detected in the lungs.

“When you look inside the lungs of nasally or parenterally primed mice 5 weeks later, the nasally primed mice have tons of IgA-secreting plasma cells under the epithelium, and the IgA bathes the lung light,” Iwaskai wrote on Twitter. “These IgA-secreting cells at 5 weeks post-priming are mostly tissue-resident cells (meaning they sit in the lungs and don’t move).”

Importantly, these nasal and pulmonary IgA responses were not observed in animals receiving the vaccine by injection. Only intranasal administration of the vaccine generated this type of immune response.

Flu vaccines have been used in these current experiments, however, researchers are now conducting similar animal tests with COVID-19 vaccines. Iwasaki says the findings suggest nasal vaccines may be more effective at producing immunity that broadly protects against many variants of an individual virus.

“These results indicate that nasal vaccines induce IgA and promote better cross-protective immunity against viral variants, and suggest their utility in the fight against COVID-19 variants of concern,” she adds.

A number of nasal inhalable COVID-19 vaccines are currently in development, and several are already in the early stages of human trials. But developing effective nasal vaccines has proven difficult, with several research dead ends over the past few decades suggesting the task may be easier said than done.

The new research has been published in the journal Sciences Immunology.

Source: Yale News

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