October 1999
SEATTLE - The Advisory Committee on Infectious Diseases has recommended that premature infants be immunized at the same chronological age as recommended for full-term babies.
Intrauterine immunoglobulin G (IgG) correlates with gestational age, making premature infants particularly prone to vaccine-preventable diseases such as pertussis. Premature babies who contract pertussis are at increased risk of severe infection, hypoxic episodes with paroxysmal coughing, long-term lung damage after infection and even death.
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Studies have shown that many health care providers do not immunize premature infants according to the same schedule as full-term babies. Reasons include the mistaken belief, by doctor or parent, that birth weight, current weight or degree of immaturity play a role in when immunizations should be given.
"When they're 2 months old, these babies still tend to be rather small," said Robert L. Davis, MD, MPH, of the University of Washington Department of Pediatrics. "That may dissuade physicians from wanting to vaccinate patients, or it may dissuade parents from being receptive to the suggestion that they get vaccinated."
In addition, "they may be ill more frequently than other children, and again, that would make physicians hesitant or parents reticent to vaccinate their kids on time," Davis said. "But vaccinating these infants is important, because they are at the highest risk for getting really sick from a vaccine-preventable disease. It's known that children are able to mount an immune response just fine if they have a mild illness, so we should grab the situation when the child is in for a mild illness and vaccinate them."
Data collected from 1991 to 1997 indicate that premature or low-birth-weight infants receive their immunizations later than full-term infants.
Improving immunization rates may be as simple as tracking immunizations. Davis said that some health maintenance organizations, private physicians offices and health departments now track who is missing an immunization, and either contact them or flag their records for the next visit. "There's fairly good evidence that these systems are effective at improving immunization rates," he said.
Physician education and simply getting children in for scheduled well-child visits may also help improve the situation.
Population-based data on premature infants from three large health maintenance organizations (HMOs) on the West Coast were studied. The main focus was on immunization levels among premature infants according to different strata of low birth weight and according to the concomitant presence of pulmonary disease, which is common among premature babies.
A total of 11,580 premature and low-birth-weight infants born between March 1991 and September 1995 were continuously enrolled at three Vaccine Safety Datalink (VSD) sites through 2 years. Data through March 1997 was analyzed. Not all infants had turned 2 at the time of the study, so 6,832 premature and low-birth-weight infants at least 2 years old who had been continuously enrolled since birth were included. Among full-term, normal-birth-weight babies, there were 173,373 enrolled at 2 months and 103,324 at 2 years.
Immunization levels were measured at 2, 4, 6, 15, 18 and 24 months for premature and low-birth-weight infants. Full-term, normal birth weight infant immunization levels were also analyzed.
With only one exception, infants with birth weights of less than 1.5 kg were not up-to-date with their immunizations.
At 6 months, 52% to 65% of infants weighing less than 1.5 kg at birth were up-to-date compared with 69% to 73% of those weighing 1.5 kg -2.5 kg and 66% to 80% of premature infants weighing more than 2.5 kg at birth. Sixty-five percent to 76% of normal-birth-weight infants were current with their immunizations at the same time.
At 2 years, 78%-86% of children born weighing less than 1.5 kg were up-to-date, compared with 84% to 89% of children weighing 15,000-25,000 g and premature babies weighing more than 25,000 g. Eighty-four percent to 88% of normal birth weight children were current with their immunizations at the same time.
Lack of routine well-child care was found to be associated with poorer immunization status. Disease severity was not found to be associated with lower immunization levels, possibly because patients with pulmonary problems may be more likely to receive non-routine care.
For more information:
- Davis RL, Rubanowice D, Shinefield HR, et al. Immunization levels among premature and low-birth-weight infants and risk factors for delayed up-to-date immunization status. JAMA.1999;282(6):547-552.
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