WEST PALM BEACH, Fla., Feb. 14 (UPI) -- An inhaled influenza vaccine appears to be more potent in protecting children younger than 5 from the flu than does a vaccine that requires injections.
In an international study, 153 cases of influenza occurred among children who received the nasally inhaled, live, attenuated vaccine FluMist (MedImmune), while 338 flu cases were recorded among children who were injected with an inactivated flu vaccine, researchers reported Wednesday.
The report will be published in Thursday's editions of the New England Journal of Medicine.
"There were 54.9 percent fewer cases of cultured-confirmed influenza in the group that received live attenuated vaccine than in the group that received inactivated vaccine," said Robert Belshe, professor and director of the division of infectious disease and immunology at Saint Louis University.
However, the higher rate of success in preventing children from contracting the flu does come with some complications. Belshe noted that higher rates of wheezing were seen among patients who were given the live vaccine, especially in children with a history of wheezing and in children who were under a year of age.
In the children ages 6 months to 11 months, about 3.8 percent of those getting the live vaccine developed wheezing compared with 2.1 percent of the children who got the inactivated influenza virus, he said. Although those numbers of children were small, the difference was statistically significant.
"Vaccines should have minimal side effects because they are being given to people who are not sick," said Carolyn Bridges, associate director of science in the influenza division of National Centers for Immunology and Respiratory Diseases at the Centers for Disease Control and Prevention in Atlanta.
"The Food and Drug Administration with have to weigh the success of the live vaccine in protecting against the flu against the side effects associated with it before deciding whether to license the vaccine for children from 6 months to 59 months of age," Bridges told United Press International.
Current guidelines call for vaccination of children ages 6 month to 59 months, plus individuals at high risk of infection with influenza -- generally the elderly and those with weakened immune systems.
"We also believe that if you live in a household where there is a person who is at high risk of influenza, all members of the household should be vaccinated," said Bridges, co-author of an editorial in the journal that accompanies Belshe's report. She said that was especially true for households where there are babies under the age of 6 months.
"We do not vaccinate children under 6 months of age against influenza," she explained. But if all the members of the household are vaccinated, the infant would receive "herd" protection against the disease, she said.
In the study, Belshe and colleague enrolled 4,179 children to receive the live vaccine and 4,173 children to receive the inactivated vaccine. Children in North America who received inactivated vaccine were given Fluzone (Aventis Pasteur); children who were assigned to receive inactivated vaccine who lived in Europe and the Middle East, were inoculated with Vaxigrip (Aventis Pasteur).
Children were observed to determine how well the vaccine protected them against influenza and also how often adverse side effects occurred. Children who had a history of wheezing or asthma-like diseases appear to be at greater risk of wheezing within 42 days of inhaling the live vaccine. Infants under the age of one years were more likely to need hospitalization within 180 days of received the live vaccine that were children of the same age who received the inactive product, Belshe said.
"The live attenuated influenza vaccine we used has many of the characteristics that are desirable for the control of epidemic influenza," Belshe said. However, he suggested that until scientists could determine why the incidence of wheezing was higher in children with a history of wheezing and why serious adverse events occurred more often in younger children, caution should be used in delivering the vaccine to that group.
"At this point in time," Bridges told UPI, "there is not likely to be any change in practice regarding who gets the vaccine because the live vaccine is not yet approved for children 6 months to 5 years of age."
If that approval occurs, then doctors and parents of children will have to weigh the risks and benefits of treatment with either of the vaccines. She noted that even though the live vaccine reduced the risk of contracting influenza, neither vaccine was 100 percent protective.
