A smaller dose of flu vaccine may be successful in preventing the virus from striking adults age 18 to 60. Some researches said they were hopeful that this would lead to an increase in the availability of the vaccine in light of the recent shortages throughout the U.S.

The smaller dose contains only 40 percent of the vaccine given normally and is delivered between the layers of skin rather than shot directly into a muscle as traditionally done. Experts also said the shot was less painful when delivered this way.

Unfortunately, the diluted flu shot has not been found to be effective for those most at risk for the virus: the chronically ill and those over the age of 60. Officials are hopeful that those who act as caregivers for people at risk can be vaccinated and thereby not spread the disease to those at risk.

'We are learning that the same size dose doesn't seem to fit all ages,' said Dr. Robert Belshe, the leader of the study in a statement. 'Younger people may need less vaccine, and older people may need more vaccine.'

Belshe was hopeful that the available dose for people age 18-60 can be increased by 2 1/2 times.