Infants who are immunized in the afternoon sleep better during the first 24 hours after immunization than those immunized earlier in the day, particularly if they have elevated temperatures.
The increased sleep duration with afternoon vaccination may signal better antibody response, postulate researchers of a randomized controlled trial.
The study was designed to compare the effects of acetaminophen on infant sleep duration after immunization. Seventy of the infants had their sleep monitored by ankle actigraphy in the 24 hours before and 24 hours after their first immunization occurring about age 2 months.
Infants slept an average of 69 minutes more in the 24 hours after immunization compared with the 24 hours before immunization. There were 2 significant correlates of the increase in sleep duration after immunization: higher mean temperatures in the 24 hours after immunization and immunization later in the day. Infants immunized after 1:30 pm had greater increases in sleep quantity than those immunized earlier in the day. In fact, many of the infants immunized earlier in the day slept less after immunization than they had in the previous 24 hours.
Temperature increase is considered a marker of immune response, the researchers note, and even brief periods of sleep restriction could disrupt the antibody response after immunization.
When controlling for other factors, acetaminophen administration was not a significant predictor of sleep duration.