Most people think of influenza as a common health problem -- not a serious condition.

Yet an influenza infection can be deadly, especially in older adults, young children and people with weak or failing health.

Every year, less than half of all adult Americans who should have a flu vaccine actually get one.

The vaccine is injected into the muscle of the upper arm. The injection is painful. It can leave redness on the skin and cause swelling, temporarily enlarging the area.

In the United States, flu season usually begins in late autumn and continues until spring.

Now, scientists have developed a treatment that may soon take the pain out of flu vaccines. And, they hope it will increase the percentage of Americans getting flu shots.

Nadine Rouphael is a professor of infectious diseases at Emory University School of Medicine in Atlanta, Georgia. She was the lead investigator for clinical testing of the influenza skin patch.

Rouphael explained that the patch has very small needles that contain the flu vaccine. She said the needles completely melt into the skin and do not leave any sharp waste afterward.

Patients wear the patch for just a few minutes. Then, the material can be thrown away.

The clinical tests took place in June 2015 and involved 100 patients. They were from 18 to 49 years old. None had received a flu vaccine during the most recent influenza season.

The patients were divided into four groups.

Health care providers or patients put on the influenza patches. Some of the patients also received the vaccine by injection. The fourth group was given a placebo, or harmless substance.

Whether the patch was put on the skin by a health care provider or by a patient, Rouphael says it was as safe and effective as the common needle injection. There were few harmful effects, including a small amount of redness and swelling, which lasted a few days.

The findings were reported in The Lancet.

The investigators wrote in their report that, six months after the vaccination, both the common needle and patch methods offered similar protection.

Nadine Rouphael says the patients who used the patch liked it.

"We do have a lot of people that are typically scared of needles and they're more prone or were more excited about being part of this clinical trial so they could try the microneedle instead."

Rouphael says 70 percent of those who used the patch liked it more than an injection.

The patch does not need to be kept in cool place. So Rouphael says it could be sold in stores or mailed to patients. The fact that it is painless, she notes, means more people will probably get vaccinated against the seasonal flu virus.

The Global Center for Medical Innovation manufactures the patch. The company is also investigating using the technology for other vaccines, including for measles, mumps and rubella.

I'm Alice Bryant.

Jessica Berman wrote this story for VOA News. Alice Bryant adapted it for Learning English.

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clinical – adj. of or relating to a medical treatment

patch - n. a piece of material that is worn for medical reasons

needle – n. a very thin, pointed tube that is pushed through the skin so that something, such as a drug, can be put into your body or so that blood or other fluids can be taken from it

prone – adj. likely to do, have, or suffer from something