Nasal Flu Vaccine in Kids: One Dose Is Good, but Two Are Better

For infants and children under age three, one dose of nasal influenza vaccine reduces the risk of getting sick with the flu, but two doses offer better protection, reports a study in the May issue of The Pediatric Infectious Disease Journal. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health, a leading provider of information and business intelligence for students, professionals, and institutions in medicine, nursing, allied health, pharmacy and the pharmaceutical industry.

Led by Dr. Humberto Bracco Neto of Federal University of São Paulo, Brazil, the new study adds to the evidence that the nasal live attenuated influenza vaccine (LAIV) is safe and effective in reducing the risk of influenza—as well as accompanying ear infections—in infants and young children.

Data Support Increased Use of Nasal Influenza Vaccine in Young Children

The study included 3,200 children, aged six months to three years, in South Africa, Brazil, and Argentina. In the first year of the study, the children were randomly assigned to receive one or two doses of LAIV, or to receive inactive placebo vaccines. In the second year, they received one dose of either LAIV or placebo.

Either one or two doses of nasal flu vaccine reduced the children's risk of becoming ill with influenza. Compared to children receiving placebo vaccine, protection against similar strains of influenza virus was 74 percent for children receiving two doses of LAIV and 58 percent for those receiving one dose. Protection rates remained high during the second year—but somewhat higher for children who received one more dose of LAIV during year 2.

As in previous studies, LAIV caused few complications or side effects. Among children receiving the nasal flu vaccine, the rate of adverse reactions was not significantly higher than for children receiving the inactive placebo.

Middle Ear Infections Decrease As Well

At least in the first year, children receiving LAIV were also less likely to develop middle ear infections (acute otitis media)—a common complication of influenza in young children. Influenza vaccination did not reduce the risk of lower respiratory infections, such as pneumonia.

Influenza is a major cause of illness, doctor visits, and hospitalization in infants and young children. Beginning in the 2008-09 flu season, U.S. recommendations call for two doses of influenza vaccine for all children aged six to eighteen months. However, vaccine recommendations aren't always easy to meet—it is estimated that less than half of patients receive the recommended two doses. That makes it important to know how much protection is afforded by a single dose of flu vaccine.

Consistent with previous studies, the new results suggest that even a single dose of nasal influenza vaccine provides good protection against influenza in infants and toddlers. In the first year, two doses of LAIV are more effective than a single dose. Protection lasts into the next year as well, although risk of influenza is lower if vaccination is repeated.