Nasal Sprays, Injections Both Provide Flu Protection for Toddlers

Children younger than 3 years old receive the same protective antibody response from the recommended 2 doses of licensed seasonal influenza vaccines regardless of whether the two doses are injected by needle, inhaled through a nasal spray, or provided through one dose of each in any order, according to research published in the August 15, 2011 issue of The Journal of Infectious Diseases.

In the study, which sought to determine whether giving 2 different types of vaccines can be just as effective as 2 matching vaccines, researchers found that young children who received at least 1 dose of the nasal spray vaccine—a live, attenuated influenza virus vaccine (LAIV)—produced a wide array of immune T cells. Stimulating broad T-cell responses may be important for protection against many diverse flu strains.

Influenza vaccinations for young children are provided in a 2-dose, prime-boost combination. The first vaccine dose is designed to prime the immune system to produce a favorable antibody response, and the second vaccine dose is the “boost” designed to spur an immune response, according to the study, which was led by Daniel F. Hoft, MD, PhD, of Saint Louis University School of Medicine in St. Louis, Missouri.

“Severe complications from seasonal influenza can be devastating to young children,” said Anthony S. Fauci, MD, director of the National Institutes of Health’s National Institute of Allergy and Infectious Diseases, in a statement. “This study provides initial evidence that the prime and booster doses for these young children can be different types of flu vaccines and still provide adequate protection against matching seasonal flu strains.”

The trial took place during the 2005-2006 and the 2006-2007 flu seasons and involved 53 children aged 6 to 35 months who had not received an influenza vaccine before. During the study, all participants received an initial dose of licensed seasonal flu vaccine and a booster dose 1 month later. In 2 groups, the vaccines matched, with children receiving 2 injections of a trivalent, inactivated vaccine (TIV) injection or 2 LAIV nasal spray vaccines. Children in the other 2 groups received a combination of vaccines, with a dose of LAIV given either before or after TIV.

“Kids who have never been immunized against flu are generally advised to receive two doses of inactivated or live, attenuated vaccine to ensure adequate antibody responses,” said Dr. Hoft. “Vaccination schedules combining one dose of TIV with one dose of LAIV have not been recommended because clinical studies of these combinations have not been done previously. However, due to vaccine availability or other factors, children may sometimes be given a mix of vaccines.

The researchers found that all 4 dosing patterns were safe and induced similar levels of protective antibodies. However, when the investigators looked at responses from the T-cell arm of the immune system, a striking difference emerged. They could not detect influenza-specific T cells in children who received only TIV, according to Dr. Hoft. However, he added, “The kids who received at least one dose of LAIV nasal spray vaccine produced significant amounts of three important T-cell subtypes that are likely to confer additional protection beyond that afforded by antibodies alone.”