Oct. 4, 2004 (Boston) -- Here's a potential shot in the arm for efforts to improve flu vaccine coverage of toddlers: New studies show that kids who are given one dose of flu vaccine in the spring and a second one in the fall appear to get the same protection from the flu as children who receive the standard two doses given one month apart in the fall.
The CDC recommends that all children between the ages of 6 months and 2 years be immunized against the flu (the vaccine is not approved for newborns). The CDC also recommends that all children younger than 9 years old who are being vaccinated against flu for the first time receive two doses, because the immune system is primed for action by the first dose, but requires a second dose in order to mount a strong defense against infection with the flu virus.
Splitting the doses into spring and fall would be more convenient for parents, because they could have the kids vaccinated during regular six-month checkups, when they receive a raft of vaccinations against other childhood diseases anyway.
But because influenza is infamous for being a viral quick-change artist, there is some question whether a spring-fall vaccine schedule would adequately protect children from the current year's flu strain.
The flu virus is extremely adept at [changing], allowing new strains of the virus to crop up nearly every year. This means that scientists who develop the vaccine must make educated guesses about what to put into each year's version of the vaccine to protect people against the virus types that are likely to be circulating that year.
By a quirk of fate however, researcher Kathleen Neuzil and colleagues from University of Washington and Duke, planned and implemented a study testing the spring-fall schedule versus the standard schedule during one of those rare periods when the flu vaccine stayed the same from one year to the next.
2nd Shot Still Strong in the Fall
In the study, the researchers gave the flu vaccine on a spring-fall schedule to 114 toddlers, and in two fall doses one month apart to 145 others. They took blood samples before and after the second vaccination to see how well the immune systems of the children were responding to the vaccines. The flu vaccine uses an inactivated form of the virus to stimulate the immune system into attacking when it encounters the real thing.
The investigators found that in both groups there was only a weak immune system response (to develop antibodies to fight off an infection with the flu) following the first vaccination and a strong response after the second, regardless of whether the second dose was given one month or six months after the first.
There were no significant side effects from the vaccinations in the study, and nearly two-thirds of parents surveyed said they preferred the spring-fall schedule to the standard schedule. Moreover, 83% of parents said they'd rather that their kids get the flu vaccine along with all the other shots they have to take in their early years.
The researchers are continuing the study, and hope to have more definitive answers next year about whether the spring-fall strategy will work when kids receive two slightly different forms of the flu vaccine.
WebMD asked a pediatric infectious disease specialist who was not involved in the study whether splitting flu shots into two doses six month year apart could provide adequate protection against the flu, or whether it was a case of trading protection for convenience.
"I don't think there's going to be a tradeoff with spring-fall immunization," says Richard J. Whitley, MD, professor of pediatrics in the department of pediatric infectious diseases at the University of Alabama at Birmingham. He notes that the only concern will be to be sure the vaccines accurately protect against the current strain of the flu.
The study was funded by an unrestricted grant from Aventis Pasteur, Inc., manufacturer of an influenza vaccine.
Neuzil is a recipient of research grants and support from Aventis Pasteur.