Giving flu vaccine to toddlers in the spring and fall guards against infection

Giving flu vaccine to toddlers in the spring and fall guards against infection and is easier on parents than the fall schedule of two doses administered a month apart, found researchers from Duke University Medical Center and the University of Washington.

The study compared the immune response in toddlers aged six to 23 months who received a flu shot in the spring and one in the fall, to the response of those who received fall shots separated by one month. The Centers for Disease Control and Prevention this year issued a recommendation for flu vaccination for all children in this age group. Children given spring-fall shots – up to six months apart – were as well-protected as those who received two shots in the fall, the study showed. The spring-fall group also completed their immunization earlier than toddlers in the fall group. A survey of parents showed 66 percent preferred the spring-fall schedule.

The results were presented Oct. 2, 2004, at the annual meeting of the Infectious Diseases Society of America. The study was sponsored by an unrestricted grant from Aventis Pasteur, which manufactures flu vaccine.

"Kids less than two years old have a higher risk of significant complications from flu that require hospitalization. Trying to get them all in for their shots in fall is logistically tough and not necessarily convenient for parents. If we can get more kids immunized by making the schedule more convenient for parents, then we'll prevent more severe flu complications," said Emmanuel Walter, M.D., associate professor of pediatrics at Duke University Medical Center.

In the trial, the spring dose given during the study was the 2002-2003 vaccine and the fall dose was the 2003-2004 vaccine. Both vaccines coincidently had similar antigen components. Antigens are substances that stimulate an immune response. This year, the researchers will compare the immune protection afforded by the spring-fall schedule when the inactivated flu vaccine changes significantly from year to year. Toddlers enrolled in the study this spring received the 2003-2004 vaccine and will receive the 2004-2005 vaccine this fall.

"I don't want practitioners to adopt this until the study is complete because we have not tested this schedule when the vaccine antigens changed from year to year. The key result will be what happens this year when the antigens change," Walter said.

The CDC recommends that children younger than nine years old should receive two doses of inactivated flu vaccine if not previously vaccinated, because they do not develop a strong immune response to a single dose. Physicians are advised to administer the two shots one month apart. This dosing schedule strains the capacity of primary care centers and may delay full vaccination for children until flu season is already underway, Walter said.

Children in the standard fall group completed their immunizations two months later than the spring-fall group during the study. Ninety-five percent of children in the spring-fall group received two doses by Oct. 2, while 95 percent of those in the standard group finished two doses by Dec. 2.

Vaccinating children less than two years old is especially important because they are more likely to develop flu complications requiring hospitalization. For example, gastrointestinal symptoms such as nausea, vomiting and diarrhea are much more common in children than adults. Children are also contagious longer than adults, shedding virus for more than a week.

"This new schedule could potentially increase rates of influenza immunization in young children, a group at high risk for complications of influenza," said Janet Englund, M.D., associate professor of pediatrics at the University of Washington and Children's Hospital and Regional Medical Center.

Closely-spaced clinic visits can also be inconvenient for parents. A survey of parents who participated in the study found 66 percent preferred the spring-fall schedule to the standard schedule. Eight percent had no preference, and 26 percent preferred the standard two doses in fall.

"Providing influenza vaccine to children at the same time as other childhood vaccines on a spring-fall schedule was preferred by parents and decreased their number of office visits," Englund said.

The study also examined flu vaccine safety in young children. There were no severe adverse events associated with the vaccine during the study. The most common side effects were irritability, sleep change, low grade fever and pain and tenderness at the injection site. There were no differences in side effects between the spring-fall group and the standard fall dose group of toddlers.

"This suggests the vaccine is pretty well-tolerated in this age group," Walters said.

Co-authors on the study include Mary Fairchok, M.D. of the Madigan Army Medical Center in Tacoma, Wash.; Kathleen Neuzil, M.D., University of Washington; and Arnold Monto, M.D., University of Michigan.