Changes in measurement of Haemophilus influenzae serotype b (Hib) vaccination coverage --- National Immunization Survey, United States, 2009.

The National Immunization Survey (NIS) has introduced a new method for measuring Haemophilus influenzae serotype b (Hib) vaccination coverage. Since its inception in 1994, NIS has considered a child aged 19-35 months to be fully vaccinated with Hib vaccine if the child had received 3 or more doses of any Hib-containing vaccine (3+Hib), regardless of vaccine product type received. However, for some Hib vaccine product types, 4 doses are needed to be fully vaccinated. Because NIS data have not distinguished between Hib vaccine product types, a child who received 3 doses of a vaccine product that requires 4 doses was misclassified as fully vaccinated. Since January 2009, NIS has requested that vaccination providers report data on Hib vaccine product types. Using this new information, two new measures were created: 1) primary series completed and 2) fully vaccinated (primary series completed plus booster dose). To determine the effects of the new method, CDC used preliminary data from the first half of 2009 NIS to compare the new measures with the previous 3+Hib measure. The findings, which were influenced by a nationwide shortage of certain Hib vaccine types, indicated that 92.9% of children aged 19-35 months in the United States had received the primary Hib series according to interim recommendations of the Advisory Committee on Immunization Practices (ACIP), and 56.9% were fully vaccinated. Using the previous method, 82.9% were fully vaccinated (3+Hib). When interpreting Hib vaccination coverage estimates and analyzing trends with NIS Hib vaccination coverage data in the future, analysts and state immunization programs should be aware of this change in Hib measurement.