What's a universal flu vaccine, and how close are we to developing it?

As flu season approaches, medical professionals are preparing to dole out some 166 million shots to vaccinate Americans against the disease. But flu vaccines are only about 40-60 percent effective and don't always work for the elderly or when they're delivered through the nose.

But scientists think we're close to developing a universal flu vaccine that might only need to be administered as little as once during a person's lifetime. If it works, it might protect everyone on Earth from flu pandemics.

Humans get the flu when a protein from an influenza virus attaches to our cells. Typical flu vaccines force our immune system to create antibodies that recognize that protein and wrap around its head. But the head frequently changes to avoid those antibodies, which eventually makes vaccines ineffective.

SEE MORE: The Future Of Flu Vaccines Doesn't Involve Getting A Shot

However, that protein head is also attached to a stalk that changes less than heads do. They're much harder for antibodies to reach, but scientists think if they figure out how to get to the stalk, they can develop a universal vaccine.

It could be in your system sooner than you think, too. The director of the National Institute of Allergy and Infectious Diseases said he was optimistic that we could see a universal vaccine as early as 2020 or 2025.

More on viruses:

Recent norovirus outbreaks, more on norovirus
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Recent norovirus outbreaks, more on norovirus
This transmission electron micrograph, TEM, revealed some of the ultra structural morphology displayed by norovirus virions, or virus particles. Noroviruses belong to the genus Norovirus, and the family Caliciviridae. They are a group of related, single-s
Amanda T. Harrington, PhD, assistant professor of clinical pathology at UIC, tests specimens on Tuesday Jan. 12, 2016 using the Verigene System, made by Nanosphere based in Chicago, which helps medical professionals identify gastrointestinal infections like norovirus on the molecular level. UIC is one of the universities/hospitals that has the system. (Phil Velasquez/Chicago Tribune/TNS via Getty Images)
The Norovirus has increased tenfold in Colorado in the last 6 years, with most of the outbreaks showing up in nursing homes. Raquel Rivera cleans the private rooms and the common areas at Chateau des Mons Care and Assisted Living in Englewood, and has a rigorous cleaning regime. Since the home had an outbreak of the virus just over a week ago, along with her everyday routine of soap and disinfectant, Rivera wipes everything down with a bleach solution. She will use the bleach for at least two weeks after the conclusion of the last outbreak. Kathryn Scott Osler, The Denver Post (Photo By Kathryn Scott Osler/The Denver Post via Getty Images)
WASHINGTON, DC - June 10: Rep. Diana DeGette, D-Colo., and Rep. Gene Green, D-Texas, during the House Energy and Commerce Subcommittee on Health markup of a bill to amend the Federal Food, Drug and Cosmetic Act with the goal of improving the safety of food in the global market. (Photo by Scott J. Ferrell/Congressional Quarterly/Getty Images)

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