New York, Aug 11 (IANS): Researchers have developed a method to modify the nasal spray flu vaccine to make it effective for those under two and over 49 - two groups for which the vaccine is not approved.

Currently nasal spray flu vaccine that uses a live but weakened form of the virus is not recommended for those under two as it is thought to be too strong to be safe for kids, and too weak to be effective for the elderly.

The researchers said they have now determined that the virus can be weakened (for young children) or strengthened (in older people) enough to create an appropriate immune response in people of all ages.

"We think we can use our molecular, rational design approaches to make a better flu vaccine for people who really need it," said study leader Andrew Pekosz, associate professor at Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, US.

"We can do it in a sophisticated and accurate way, not in a blind manner, which is how these vaccines are usually developed," Pekosz noted.

Flu vaccines are less effective in people as they age and those over the age of 60 are more likely to get the flu and more likely to suffer serious complications.

"We do not have a really good effective vaccine in the elderly," Pekosz said.

"Even the injectable version does not work as well in that population. And they are the ones who need it the most. We hope our research can get us closer to having effective flu vaccines for any age," Pekosz noted.

Children aged six months to two years can receive an injectable flu vaccine, but the nasal spray vaccine is recommended in children between the ages of two and eight because it is believed to give better protection than the shot.

In their effort to make the nasal spray vaccine available for people of all ages, the researchers studied the weakened flu virus that is the basis for the nasal spray vaccine in cells from human nasal and sinus cavities.

The new vaccine should be ready for testing within six to 12 months for both the oldest and youngest, said the study published online in the journal Vaccine.