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Vaccination schedule for infants caused no neuropsychological harm
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Timely immunization with all recommended childhood vaccines during infancy had no detrimental effects on neuropsychological development later in life, according to results of a recently published study.
Despite a marked decline in vaccine-preventable diseases, parents remain apprehensive about the safety of immunization. The discredited link between vaccines and autism is at the heart of many parents’ concerns, but others also worry that a cramped vaccination schedule early in life inundates an infant’s immune system and causes long-term adverse effects.
“Although the number of parents who completely refuse vaccines remains low, many families are requesting alternative immunization schedules that space out and delay receipt of the recommended childhood vaccines,” wrote researchers from the University of Louisville School of Medicine in Kentucky.
The researchers set out to determine whether children who received vaccines on a delayed schedule demonstrated different neurodevelopmental outcomes than children who were immunized on time.
The researchers used information from a previous Vaccine Safety Datalink study on thimerosal exposure for their analysis. Children in the study were born between 1993 and 1997 and should have received at least two hepatitis B (HepB) vaccines, three diphtheria and tetanus toxoids and acellular pertussis vaccines, three Haemophilus influenzae type b vaccines, and two polio vaccines by the study’s conclusion. They then underwent assessment for 42 neuropsychological outcomes when aged 7 to 10 years during 2003 to 2004. Timely vaccination was defined as immunization within 30 days of the recommended age.
Of 1,047 children, 491 were vaccinated on time; 235 received all recommended vaccines but not on time; and 311 did not receive all recommended vaccines. HepB and polio vaccines had the highest percentages of timely vaccination, whereas DTaP and Hib had the lowest, according to the researchers.
Results indicated that timely vaccination was associated with better performance on 12 of 42 outcomes. Children who were immunized on time had higher scores on the Boston Naming Test, grooved pegboard, metacognition and Connors’ Teacher Ratings Scale for hyperactivity and inattentiveness, the researchers said. They also demonstrated better verbal skills and had higher IQs. Children who were not immunized on time, however, did not perform better on any outcomes.
The researchers also said children who received timely vaccination scored one point higher on the Developmental Neuropsychological Assessment speeded naming test and 2.7 points higher on the Wechsler Abbreviated Scale of Intelligence performance IQ.
Results also revealed that children who completed their vaccination series between 154 and 191 days (the most timely group) performed statistically better for 15 outcomes when compared with children who either did not complete the series or completed the series between 263 and 363 days (the least timely group).
“This study provides the strongest clinical outcomes evidence to date that on-time receipt of vaccines during infancy has no adverse effect on neurodevelopmental outcomes 7 to 10 years later,” the researchers wrote. “These results offer reassuring information that physicians and public health officials may use to communicate with parents who are concerned that children receive too many vaccines too soon.”
Smith MJ. Pediatrics. 2010;125:1134-1141.
The notion that vaccines cause neurological or psychological delays, including autism, has gone through several stages. First, there was the fear that the combination measles-mumps-rubella vaccine was responsible. Next was born the notion that thimerosal, an ethylmercury-containing preservative in vaccines, was the cause. About 18 different studies during the past decade have failed to support either of these hypotheses. More recently, the hypothesis has morphed to the notion that too many vaccines given too soon were the problem. The study by Smith and colleagues, failing to find an association between the timing of vaccines and neurological problems, is the first to examine this most recent hypothesis and, as such, is an important contribution to what we can tell parents about the safety of vaccines.
– Paul Offit, MD
Infectious Diseases
in Children Editorial Board