The final dose of the vaccine known as DTaP is especially important because
it helps maintain immunity during the preschool years against easily transmitted
diseases like whooping cough, say Tara W. Strine, M.P.H., of the Centers for
Disease Control and Prevention and colleagues.
The researchers suggest that physicians stress the importance of the final
dose to parents with children who have received previous late doses. They also
note that updated immunization records and reminder or recall systems may help
solve the problem.
The U.S. childhood immunization schedule calls for children to receive DTaP
doses at 2 months, 4 months, 6 months and 15-18 months. Previous research indicates
that the fourth dose is the most commonly missed.
After examining data from a large nationwide survey of immunization coverage,
Strine and colleagues determined that children who received second and third
DTaP doses on time were more likely to receive their final dose on time.
Other factors, including as the mother’s age, her education level, whether
the child was a firstborn and the number of available vaccine providers, were
also associated with a child’s likelihood of receiving the final DTaP
dose on time.
“However, none of these factors was a stronger predictor of receipt
of the fourth DTaP dose than timeliness of dose three,” says Strine.
A late third dose also meant that the final dose was given incorrectly, according
to the researchers. Immunization guidelines suggest a six-month interval between
the third and final dose, but those who received the third dose too late often
got the final dose too soon after the third one.
Children who receive these “invalid” final doses need yet another
vaccination to make sure they are adequately protected, and may have an increased
rate of bad reactions to the vaccine.
“Thus, an invalid dose four of DTaP represents not only wasted vaccine,
time and money, but also unnecessary increased risk of adverse reactions and
difficulty in completing the series by 18 months,” Strine says.
The data in the study come from 2001, amid a DTaP vaccine shortage that prompted
a federal advisory committee to recommend delaying the final dose if local
vaccine stockpiles were low. But the link between the late third dose and missed
final dose was similar in data collected in 1999, Strine and colleagues note.
