Immunizing young children against influenza is an important public health objective, particularly since children are among the most severely affected during flu outbreaks. Recently, the Centers for Disease Control and Prevention recommended that all children 6 months of age and older should be vaccinated, but repeated studies have demonstrated that two vaccinations are required for a sufficient protective response in children younger than 9 years old receiving their first dose of influenza vaccine. Previous trials have also shown that the immune response in very young children (e.g., 2 months old) is less robust than in older children, but it remains unclear whether that is due to an immature immune system or diminution of response due to passively acquired maternal antibodies.
In order to assess the effect of age on immune response to the flu vaccine, VIDD affiliate investigator Dr. Janet Englund and colleagues evaluated the immune response in the youngest group for which there is a currently approved vaccine. To do this, they reevaluated data previously acquired in 2003-2004 in a study of immune responses to the flu vaccine in children aged 6-23 months depending on the timing of vaccinations, sorting the data by age group instead of vaccination season. Although there was some variability in response between individuals, the researchers found that antibody responses to the vaccine tended to increase with increasing age. However, even the lower-level responses in the youngest age group were sufficient to confer some protection, supporting the CDC recommendation to vaccinate against flu as early as 6 months of age.
Walter EB, Rajagopal S, Zhu Y, Neuzil KM, Fairchok MP, Englund JA. Trivalent inactivated influenza vaccine (TIV) immunogenicity in children 6 through 23 months of age: do children of all ages respond equally? Vaccine. 2010 Jun 17;28(27):4376-83.