Children younger than 3 years old receive the same protective antibody response from the recommended two 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 researchers funded by the National Institutes of Health.
Doctors usually give young children two matching vaccines, and one goal of the study was to determine whether giving two different types of vaccines works just as well.
In addition, the researchers found that young children who received at least one dose of the nasal spray vaccine—a live, attenuated influenza virus vaccine (LAIV)—made 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 two-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.
Complications
“Severe complications from seasonal influenza can be devastating to young children,” said Anthony S. Fauci, M.D., NIAID director. “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 study was conducted at vaccine and treatment evaluation units (VTEUs) funded by the NIH’s National Institute of Allergy and Infectious Diseases (NIAID). Daniel F. Hoft, M.D., Ph.D., and his colleagues at the Saint Louis University VTEU, along with other VTEU investigators at Vanderbilt University in Nashville, and the Cincinnati Children’s Hospital, co-authored the report, online in The Journal of Infectious Diseases.
The trial took place during the 2005-2006 and the 2006-2007 flu seasons and involved 53 children aged 6 to 35 months. Study participants were divided into four groups of roughly equal size. None of the children had received an influenza vaccine before.
During the study, all children received an initial dose of licensed seasonal flu vaccine and a booster dose one month later. In two groups, the vaccines matched, with children receiving two injections of a trivalent, inactivated vaccine (TIV) injection or two LAIV nasal spray vaccines. Children in the other two groups received a combination of vaccines, with a dose of LAIV given either before or after TIV.
Two doses
“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,” noted Dr. Hoft, director of the division of infectious diseases, allergy and immunology at Saint Louis University. “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,” he added.
The researchers found that all four 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.
But, 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.”
