Preterm infants of the right chronological age need to be immunized to protect them from vaccine-preventable diseases. Occasionally, these infants experience adverse events such as apnea, bradycardia, arterial desaturation, or other symptoms following immunization.1

A recent study confirmed previous research findings that preterm infants who have apnea in the 24 hours prior to immunization are highly likely to have apnea in 48 hours postimmunization.2 This is the rationale for immunizing former preterm infants several days before discharge from the NICU, so that they can be monitored for a period of time following vaccinations. However, this study, conducted in Northern California, also found that risk factors other than preimmunization apnea predicted apnea in the 48 hours after immunization. These risk factors were higher severity of illness at birth, younger age at immunization, and weight less than 2 kg. Two of the infants in the cohort who had at least 1 of these risk factors had been discharged shortly after a vaccination, developed apnea at home, and were readmitted to the hospital for apnea.

The most important risk factor for postimmunization apnea is still the occurrence of apnea during the 24 hours preceding the vaccination. For infants in the NICU without apnea during the 24 hours immediately before immunization, younger age, smaller size, and more severe illness at birth are important predictors of postimmunization apnea. This study supports cardiorespiratory monitoring of susceptible infants for at least 48 hours after they receive immunizations.2

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