This study, which looks at the health records of 1,047 children, is the first to evaluate the long-term neuropsychological impacts of multiple vaccinations received in the first seven months of life.
“Some parents request alternative immunization schedules as a precaution against widely publicized, but unfounded concerns about vaccines,” explained lead author and pediatric infectious diseases specialist Michael J. Smith, M.D., M.S.C.E. “This study suggests that delaying vaccines does not give infants any advantage in terms of brain development.”
In fact, varying the immunization schedule may be dangerous for infants. “We know that delaying vaccines increases newborns’ risk of contracting potentially deadly diseases like pertussis,” added co-author Charles R. Woods, M.D., M.S., UofL Pediatric Infectious Diseases.
Using records collected for a previous VaccineSafety Datalink study of thimerosal (methylmercury) exposure, researchers compared children’s performance on 42 neuropsychological tests with the timeliness of vaccinations during their first year of life.
To be considered up-to-date, each child had to receive at least two hepatitis B, three diphtheria-tetanus-pertussis (DTP), three Haemophilus influenza type B (Hib) and two polio vaccines on time during the first seven months of life. The developmental tests, given when the children were between the ages of 7 and 10, included assessments of speech and language, fine motor coordination, behavior regulation, general intellectual functioning and other abilities.
Two separate analyses were performed. In the first, children with timely receipt of vaccination were compared to all other children in the study who had delays in receipt of one or more doses. In a second analysis, children who received the maximum number of vaccines in the first seven months of life were compared to those who received the fewest vaccines in the study group.
Researchers found no evidence to suggest that multiple vaccines in the first year of life affect a child’s cognitive abilities later. In fact, children who received each dose of each vaccine on time performed better on two of the 42 tests, after adjustment for familial and socioeconomic factors. Those who missed or were late on one or more doses of vaccine did not perform better on any test.
The infant immunization schedule has changed over the past decade so more studies are needed to confirm this study’s implications for new generations of babies. For example, today’s newborns receive two additional vaccines and one that has been reformulated. Still, today’s infants’ immune systems are exposed to fewer vaccine antigens than they were during the period covered by this study, so the findings are likely to be similar. To date, there has never been any evidence in clinical studies that receiving all recommended shots on time causes harm of any type.
“As the visible threats of vaccine-preventable diseases have decreased, parental concerns about vaccine safety have increased,” Smith said. “I hope this study will reassure parents that vaccinating their children is not just safe but the right thing to do to protect their children against potentially deadly diseases.”