To assess coverage with PCV13, CDC collected data from the eight state and city-based IIS sentinel sites.4 Those collaborating sites include parts of Arizona, Colorado, Michigan, Minnesota, Oregon, and Wisconsin, all of North Dakota, and New York City, and include nearly 2 million children aged <6 years. Data on receipt of PCV13 were collected from March 2010, when PCV13 was first recommended, through June 2011 on children aged 0 through 11 months, 12 through 23 months, and 24 through 59 months as of March 2010, by primary PCV7 series completion status. A complete primary PCV7 series was defined as ≥4 doses, if the fourth dose was administered at age ≥12 months; 3 doses, if the third dose was administered at age ≥12 months; 2 doses, if both doses were administered at age ≥12 months; or 1 dose, if administered at age 24 to <60 months. Overall estimates were calculated by averaging unweighted site-specific estimates. Additionally, to evaluate the overall transition from PCV7 to PCV13, all sites reported the total number of doses administered weekly, by PCV type, during March 7–August 21, 2010.