Trends in Compliance with Two-Dose Influenza Vaccine Recommendations Among Children Aged 6 Months Through 8 Years

BACKGROUND:  To achieve high levels of vaccine-induced antibodies and decrease the risk for illness caused by virus strains that are antigenically similar to those strains included in the vaccine, some children aged 6 months-8 years require two influenza vaccine doses. Influenza vaccination is the most effective way to protect children from influenza and its complications. Unlike other vaccinations for children, seasonal influenza vaccine changes yearly to reflect circulating influenza virus strains that often vary from year to year; vaccine antigens change in order to protect against influenza viruses expected to cause disease during the upcoming season. Poor compliance with the two-dose vaccine regimen among those who initiate the series has been described, however limited data are available reporting recent trends. We analyzed data for >2 million children aged 6 months-8 years in each influenza season from 2007-2012 from eight Sentinel Site Immunization Information Systems to assess trends in two-dose compliance.

METHODS:  Immunization Information Systems (IIS) are confidential, computerized, population-based systems that collect and consolidate vaccination data from vaccine providers and provide tools for designing and sustaining effective immunization strategies at the provider and program level. The Sentinel Sites IIS Project is a collaborative project between CDC and selected state/city-based IIS with high data quality to conduct immunization program evaluations and estimate vaccination coverage. Two-dose compliance was calculated among children who met the following criteria: 1) were recommended to receive two doses according to the Advisory Committee on Immunization Practices and 2) who received their first vaccine dose during the season evaluated. Compliance was calculated by influenza season, age group, and influenza vaccination history.

RESULTS:  Two-dose compliance increased from 49% to 60% among 6-23 month olds from 2007-2012; no increase was observed for 2-4 (16%) or 5-8 year olds (11%). In each season, compliance was 3-12 times higher among 6-23 month olds compared to older children. Compliance was also two times higher among influenza vaccine naïve children compared to previously vaccinated children who were recommended to receive two doses.

CONCLUSIONS:  While two-dose compliance has improved among 6-23 month olds, it remains low and unchanging for older children. Access to complete influenza vaccination histories at the time of vaccination and improved messaging for providers and parents about the importance of the two-dose recommendation and about which children are eligible for two doses are needed.