Because infants are more susceptible to illnesses than older children, and their lungs are not fully formed until age 2, a winter respiratory virus could damage the lungs and immune system and increase infants' likelihood of developing asthma, Vanderbilt University Medical Center doctors say.

Children born from late August through November had up to a 30 percent greater risk of developing asthma than children born at other times, the research found.

The university's Center for Asthma Research analyzed birth and medical records of more than 95,000 children and their mothers.

The Tennessee Asthma Bronchiolitis Study followed the children from the time they were in the womb up through age 6.

"Infants, during the first six months of life, they're the most susceptible to getting the sickest with these viruses," asthma research center Director Dr. Tina Hartert told The (Nashville) Tennessean.

"After about 3 months old, the antibodies they've naturally received from the mother fall off dramatically, and they don't really begin to develop their own until about 6 months," she said.

If an infant's immune system is compromised during the peak of flu season, it could mean a future of childhood asthma, Hartert said.