December 22, 2009
Although a new study in published in the Journal of American Medicine (JAMA) finds one dose of vaccine may be effective to protect infants and children and reduce transmission of the swine flu, or H1N1, virus, not everyone agrees.
Initial reports of 2009 influenza-A (H1N1) infection in many countries have largely involved children, especially those in school. Reports have also indicated high hospitalization rates of kids less than 5 years of age in the current pandemic. The Advisory Committee on Immunization Practices also currently recommends that infants and children aged 9 years or younger receive two doses of H1N1 influenza vaccine at least 21 days apart, based on existing experience with seasonal trivalent influenza vaccines in this age group.
Researchers from the University of Melbourne, Australia assessed the effectiveness and safety of two doses of a 2009 swine flu vaccine in 370 healthy infants and children ages six-months to less than 9 years living in Australia. The children were split into groups that received a two-injection regimen 21 days apart in doses of either 15-micrograms or 30-micrograms of the vaccine.
"Our findings suggest that a single dose 15-microgram dose vaccine regimen may be effective and well tolerated in children, and may have positive implications for disease protection and reduced transmission of pandemic H1N1 in the wider population," the authors conclude.
In an accompanying editorial, Anthony E. Fiore, M.D., M.P.H., from the National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, and Kathleen M. Neuzil, M.D., M.P.H., of PATH, Seattle, write. "Even though influenza activity has decreased in recent weeks in some states, there remains the possibility of continued activity through the traditional winter influenza season and the prospect of normal winter circulation of seasonal influenza viruses." The authors of the editorial note that this pandemic has highlighted the fact the children have no measurable immunity against the H1N1 virus.
They further note that that children have been a primary source of illness in community outbreaks of pandemic influenza with more severe complications, hospitalizations and deaths from this virus than what is usually seen for seasonal influenza.
The editorial authors also urged caution at interpretation of the results of the study, saying that the vaccine administered to six-month-old infants and children younger than 3 years in this study was the equivalent of two doses of the vaccine currently licensed in the United States for this age group.
"The immunogenicity data presented...suggest that at least some children will be protected after a single 15-microgram dose of the H1N1 vaccine used in this study, but the findings cannot be generalized with confidence to all children, epidemiological circumstances in every country, or different vaccine formulations," they point out.
In conclusion, the authors write: "... it remains prudent to continue to follow current recommendations for administering two doses to infants and young children while awaiting definitive vaccine effectiveness data."
