Immunization Levels Among Premature and Low-Birth-Weight Infants and Risk Factors for Delayed Up-to-Date Immunization Status

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Abstract
Context Studies have noted that health care professionals may not conform to proper immunization schedules for premature and low-birth-weight infants in the United States. Little is known about the success of current efforts to immunize these high-risk infants. Objective To describe current immunization practices for premature and low-birth-weight infants and ascertain risk factors for poor immunization status, using large population-based data sources. Design and Setting Cohort and case-control analyses of immunization data tracked from March 1991 through March 1997 for 3 large health maintenance organizations (HMOs) participating in the Centers for Disease Control and Prevention's Vaccine Safety Datalink project. Participants A total of 11,580 low-birth-weight and premature infants were enrolled from birth to age 2 months; 6832 of these were continuously enrolled from birth to age 24 months. At age 2 months, there were 173,373 full-term, normal-birth-weight infants enrolled as controls; at age 24 months, there were 103,324. Main Outcome Measures Age-specific immunization status by prematurity and birth weight (Results At each age, infants weighing less than 1500 g at birth had lower up-to-date immunization levels than other infants. At age 6 months, 52% to 65% of infants weighing less than 1500 g were up-to-date at each of the 3 HMOs compared with 69% to 73% of those weighing 1500 to 2500 g, 66% to 80% of premature infants weighing more than 2500 g, and 65% to 76% of full-term, normal-birth-weight infants. By age 24 months, 78% to 86% of infants weighing less than 1500 g were up-to-date, significantly less than heavier infants, who had levels of 84% to 89%. Well-child preventive care strongly predicted immunization status, while concomitant pulmonary disease did not. Conclusions Our data suggest that infants born prematurely are vaccinated at levels approaching that of the general population, but levels of vaccination for very low-birth-weight infants lag slightly behind.