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MONDAY, May 24 (HealthDay News) -- Some American parents are choosing to space out and delay recommended vaccines because they're worried that their infants are getting too many shots too soon, potentially contributing to later mental health issues.
However, a study published online May 24 in the journal Pediatrics finds no neurological benefit to delaying immunizations during the first year of life.
Researchers at the University of Louisville analyzed the health records of more than 1,000 children. After comparing the kids' performance on 42 neuropsychological tests between the ages of 7 and 10 against the timeliness of vaccination during the first year of life, the researchers found no evidence that delaying vaccines gave children any advantage in terms of brain development.
"Our study shows that there is only a downside to delaying vaccines, and that is an increased susceptibility to potentially deadly infectious diseases," said lead researcher Dr. Michael J. Smith, a pediatric infectious diseases specialist at the University of Louisville School of Medicine. "We hope these findings will encourage more parents to vaccinate according to the American Academy of Pediatrics schedule, and reassure them that they're making a safe choice when they do so."
Smith said the study is the first to evaluate the long-term neuropsychological impacts of multiple vaccinations received in the first seven months of life. In the past few years, more and more parents are asking their pediatricians for an alternative vaccine schedule, "but we found that nobody had really looked at whether there are any advantages to delaying vaccines," he said.
Using publicly available records collected for a previous study of exposure to the vaccine preservative thimerosal, Smith and co-author Dr. Charles Woods reviewed the immunization records of 1,047 children born between 1993 and 1997, as well as their performance on 42 in-depth neuropsychological tests taken between 2003 and 2004. Children were classified as up-to-date if they had received at least two hepatitis B, three diphtheria-tetanus-pertussis (DTP), three Haemophilus influenzae type B (Hib) and two polio vaccines on time during the first seven months of life. A vaccine was considered on time if it was given within 30 days of the recommended age.
The developmental tests 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.
In both analyses, the researchers found no evidence to suggest that multiple vaccines in the first year of life negatively impact a child's cognitive abilities later. In fact, the first analysis revealed that children who received all their vaccines on time performed slightly better on two of the 42 tests, after adjustment for familial and socioeconomic factors. Kids who missed or were late on one or more doses of vaccine didn't do better on any test.
Vaccine expert Dr. Gary L. Freed, director of the Child Health Evaluation and Research Unit at the University of Michigan Health System, said he wasn't surprised by the findings, since "there's never been any evidence whatsoever that delaying vaccines does any good for any child." And the reason children receive so many vaccines at such young ages is because "the life-threatening diseases that they protect against are most likely to attack at these ages," he said.
The researchers pointed out that newborns now receive two additional vaccines and one that has been reformulated, so more studies are needed to confirm this study's implications for new generations of babies. However, they also noted that infants' immune systems are actually exposed to fewer vaccine antigens now than they were during the period covered by this study, so the findings are likely to be similar.
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