Delaying or Forgoing Childhood Vaccines Offers No Neuropsychological Benefit Down the Road

Pauline Anderson

May 27, 2010

May 27, 2010 — Delaying childhood vaccinations, or not getting immunized at all, does not provide any neuropsychological benefits for children at 7 to 10 years of age and might even result in poorer outcomes on some measures, a new study suggests.

The results should quell concerns of some parents that infants are overexposed to immunizations too early, said study author, Michael J. Smith, MD, MSCE, assistant professor of pediatrics in the Division of Pediatric Infectious Diseases at the University of Louisville (Kentucky) School of Medicine.

"Parents may have heard that it's not safe to give their children all these vaccines in the first year of life, but we actually looked at kids 7 to 10 years later and they’re absolutely fine," Dr. Smith said in an interview. "That's a talking point for pediatricians to have with families in the office, although it may not convince everyone."

The study was published online May 24 in Pediatrics.

Dr. Smith and his colleagues used information on 1047 children included in a previous Vaccine Safety Datalink (VSD) study of thimerosal exposure and neuropsychological outcomes. The VSD project provides important safety information for a number of childhood vaccines and has been used to assess vaccine timeliness.

Children in the cohort were born between 1993 and 1997 and underwent 42 neuropsychological tests between 2003 and 2004. The data set contains age in days for all vaccines administered during the first year of life.

Recommended 2-3-3-2 Series

Infants were considered to have completed all recommended vaccinations on time if they had 2 hepatitis B, 3 diphtheria-tetanus-pertussis (DTP), 3 Haemophilus influenza type B (Hib), and 2 polio vaccines (2-3-3-2) within 30 days of the recommended age during the first year of life. Children who did not meet this criterion were classified as having untimely vaccine receipt.

The 42 tests included assessments of speech and language, verbal memory, fine motor coordination, visuospatial ability, attention and executive-functioning tasks, behavior regulation, tics, and general intellectual functioning.

For all analyses, researchers controlled for age, sex, birth weight, poverty status, maternal IQ, maternal education, study site, cumulative ethyl mercury exposure during the first 7 months, and an objective assessment of stimulation and emotional support in the home environment.

A total of 491 of the 1047 children (47%) had timely vaccination schedules. An additional 235 (23%) received all recommended vaccines but not on time. The remaining 311 (20%) did not receive all recommended vaccines during the study period.

Hep B Shots Highest

Timely receipt of vaccines was highest for hepatitis B (83%) and polio (79%) and lowest for DTP (65%) and Hib (53%). Nine children received no vaccines at all during the study period.

In the primary analysis, timely receipt of vaccines was significantly associated with better performance on 12 of the 42 outcomes. Children with untimely receipt did not perform better on any of the outcomes.

Timely receipt remained associated with 2 outcomes after controlling for the numerous variables. Children who received their vaccines on time scored 1.08 points higher (95% confidence interval [CI], 0.16 – 2.00; P = .022) on the Developmental Neuropsychological Assessment speeded naming test, which requires rapid access to and production of recurring colors, sizes, and shapes. They also scored 2.72 points higher (95% CI, 0.91 – 4.52; P = .003) on the Wechsler Abbreviated Scale of Intelligence performance IQ, which assesses block design and matrix reasoning.

Socioeconomic status (SES) was an important factor contributing to the decrease in the number of significant outcomes from 12 to 2, said Dr. Smith. Interestingly, although lower SES was associated with less timely vaccinations, high SES was associated with absence of vaccinations. "We think this had to be intentional parental behavior," said Dr. Smith. "The general thought is that people who are concerned about vaccine safety tend to be educated and may have access to the Internet," where they read about vaccine myths.

However, Dr. Smith does not want to make too much of the finding that timely vaccinations are linked to better neuropsychological outcomes. Although the differences did meet "the magic P value criteria" of significance, he noted, "you have to be careful saying that if you get your shots you're going to be smarter; that's not the correct interpretation," he said.

The large size of the study strengthens the results, though, he said. "We were able to find this 2.7-point difference in IQ as a statistically significant result. That's how much power we had in our analysis, yet even with this number of children, there was not a single instance where the delayed kids did better."

Most vs Least Timely

In a secondary analysis, researchers compared outcomes of children with the most and least timely vaccinations. They stratified the youngsters by age in quintiles at completion of the 2-3-3-2 series and considered children in the first 2 quintiles to be the most timely vaccinated, having received a minimum of 10 vaccines in the first 7 months of life. The least vaccinated group were those who received 6 or fewer vaccine doses of any type during the first 7 months of life.

For this analysis, children with the most timely vaccines performed statistically better than children in the least timely group for 15 of the 42 outcomes, including 10 of the 12 outcomes associated with better outcomes in the primary analysis.

Children who had received vaccines later had lower family household incomes and lower percentages of mothers with college degrees. There were greater proportions of male children and single parent households in the less timely groups. These did not reach statistical significance in the primary analysis but did in the secondary analysis.

On "Front Line"

According to Dr. Smith, the inspiration for the study came from local pediatricians who provide vaccinations on the "front line," who regularly call his office wondering what to tell parents who request alternative vaccine schedules. These parents are concerned that children are developing an "immune overload" from receiving too many vaccines at too early an age, said Dr. Smith.

"That doesn't really make sense when you look at all the things in the environment — the bacteria and the viruses and the smoke and all these other things that children are bombarded with every day."

There are clearly downsides to delaying vaccines, stressed Dr. Smith. "Most importantly, your child is at prolonged risk of infectious diseases." He used the analogy of waiting until you're on the highway before buckling your seat belt. "You never know when your child will come into contact" with infectious agents, he said.

Many parents have never seen a case of measles or polio or other illnesses that have been all but eradicated. "Their doctor says their baby needs a vaccine for these diseases, which aren't even here any more, but the missing step, of course, is that the reason they're not here anymore is because babies have been vaccinated."

Study Incomplete

Reached for a comment, Kenneth M. Heilman, MD, The James E. Rooks Jr. Distinguished Professor, Department of Neurology, University of Florida College of Medicine, Gainesville, and a member of the American Academy of Neurology, said the study was somewhat incomplete.

"While in general, it is comforting to learn that vaccination does not cause cognitive disorders, I am concerned about what has not been studied," he told Medscape Neurology in an email.

For example, he said, the study did not address major disabling symptoms or signs associated with autistic disorders, including deficits in "theory of mind," the understanding of what other people might think, emotional empathy, emotional communication, and the ability to perform purposeful skilled movements. 

"There are methods for testing each of these, but when reading over this paper, I did not see that any of them were adequately tested," said Dr. Heilman.

At the same time, he stressed that vaccinations prevent serious diseases and until adverse effects are proven, children should be protected through these vaccines. "All my children and grandchildren received these vaccinations."

Dr. Smith and Charles R. Woods, MD, MS, are or have been unfunded subinvestigators for cross-coverage purposes on vaccine clinical trials for which their colleagues receive funding from Wyeth, Sanofi Pasteur, GSK, MedImmune, and Novartis. Dr Woods has received honoraria for speaking engagements from Merck, Sanofi Pasteur, Pfizer, and MedImmune and has received research funding from Wyeth and Sanofi Pasteur.

Pediatrics. 2010;125(6):1134-1141.

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