May 3 (UPI) -- A new flu vaccine administered through the nose prevents infection and offers broad protection against multiple strains of the virus, a study published Monday by the Proceedings of the National Academy of Sciences found.
The vaccine, which is delivered much like an allergy nasal spray, enhanced immune responses in the noses and throats of mice used in the study, the researchers said.
These robust immune responses provided protection against many different strains of the seasonal virus that infects more than 30 million people, and kills nearly 40,000, in the United States each year, based on Centers for Disease Control and Prevention estimates.
"Our research opens a new path for the development of needle-free and logistically simplified intranasal flu vaccines for cross-protection," study co-author Baozhong Wang said in a press release.
The results are promising because needle-free, intranasal flu vaccines may be easier and cheaper to administer and may encourage needle-phobic people to get inoculated, said Wang, a professor in the Institute for Biomedical Sciences at Georgia State University in Atlanta.
In a normal flu season, about 40% to 50% of people in the United States get vaccinated against the seasonal virus, according to the CDC.
However, that number was expected to increase during the 2020-21 flu season due to the COVID-19 pandemic, as federal public health officials urged people to get the shot so that healthcare providers could focus on treating those with the coronavirus.
Although not as deadly as COVID-19, recurring seasonal flu epidemics and potential pandemics are among the most severe threats to public health, Wang and his colleagues said.
Current seasonal influenza vaccines provide strain-specific immunity and are less effective against newly emerging forms of the virus, they said.
Intranasal vaccines are a promising strategy for combating infectious respiratory diseases, such as the flu, the researchers said.
Historically, they have been more effective than vaccines injected into muscles, like the conventional flu shot, because they can produce immune responses in respiratory tracts, preventing infection at the point the virus enters the body.
For this study, Wang and his colleagues developed an intranasal influenza vaccine using recombinant hemagglutinin, a protein found on the surface of flu viruses.
They refined the protein, which is key to the virus' ability to spread throughout the human body, to the size of nanoparticles -- or microscopc, ultrafine particles -- so that it could be delivered in a nasal mist-like form, they said.
They then tested the vaccine in mice and cell cultures, which were infected with various strains of the flu virus.
"Conventional flu vaccines predominantly induce antibody responses," Wang said.
"However, recent research demonstrates that lung resident memory T cell responses are indispensable for optimal cross-protection against pulmonary influenza infection, [and these] require vaccination by a respiratory route or influenza virus infection," he said.