Immunization levels among premature and low-birth-weight infants and risk factors for delayed up-to-date immunization status

Context Studies have noted that health care professionals may not conform t o 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- birthweight 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 tr acked from March 1991 through March 1997 for 3 large health maintenance org anizations (HMOs) participating in the Centers for Disease Control and Prev ention'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 enroll ed from birth to age 24 months. At age 2 months, there were 173 373 full-te rm, normal-birthweight infants enrolled as controls; at age 24 months, ther e were 103 324. Main Outcome Measures Age-specific immunization status by prematurity and b irth weight(<1500 g, 1500-2500 g, born at <38 weeks' gestation with birth w eight of >2500 g, or full-term with normal birth weight) and patient charac teristics associated with up-to-date status. Results At each age, infants weighing less than 1500 g at birth had lower u p-to-date immunization levels than other infants. At age 6 months, 52% to 6 5% of infants weighing less than 1500 g were up-to-date at each of the 3 HM Os 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 weighi ng less than 1500 g were up-to-date, significantly less than heavier infant s, who had levels of 84% to 89%, Well-child preventive care strongly predic ted immunization status, while concomitant pulmonary disease did not. Conclusions Our data suggest that infants born prematurely are vaccinated a t levels approaching that of the general population, but levels of vaccinat ion for Very low-birth-weight infants lag slightly behind.