Concerns about childhood vaccinations and the risk for autism persist for many parents and some members of the public. A new CDC study published in the Journal of Pediatrics (1) addressed a current concern about the relationship between autism spectrum disorder (ASD) and vaccination, which centers on the number of vaccines and vaccine antigens given to infants and children, according to the recommended childhood immunization schedule.
The study evaluated the association between the level of immunologic stimuli received from vaccines during the first 2 years of life and the development of ASD. The findings showed that neither the number of antigens from vaccines received on a single day of vaccination, nor the total number of antigens received during the first 2 years of life, is related to the development of autism.
About This CDC Study
This study is the first of its kind to evaluate the issue of "too many vaccines too soon" and the development of ASD. The study was conducted in 3 managed care organizations (MCOs), involving 256 children with ASD and 752 control children matched by birth year, sex, and MCO. In addition to ASD, researchers evaluated autistic disorder and ASD with regression and found no relationship with the number of vaccine antigens received in either of these categories.
Study data were obtained from immunization registries and medical records. The data used in this study had been collected and analyzed previously(2). Children eligible for the study were born between January 1, 1994, and December 31, 1999, and were 6-13 years old at the time of data collection.
Each child's total vaccine antigen exposure was determined by adding the number of different antigens in all vaccines that each child received in 1 day, as well as all vaccine antigens each child received up to 2 years of age. The number of vaccines and number of vaccine doses administered according to type of vaccine are shown in the Table.
Table. Antigens in Vaccines and Total Doses Administered by Vaccine Type
|Vaccine Type||Antigens per Dose||Dosesa|
|Diphtheria toxoid/tetanus-diphtheria (DT/TD)||2||14|
|DTP - Haemophilus influenzae type B (Hib)||3004||1659|
|Diphtheria-tetanus-acellular pertussis (DTaP)||4b||1165|
|Measles, mumps, rubella (MMR)||24||1093|
|aTotal vaccine doses administered in the study population from birth to 2 years of age|
|bNumber of antigens in DTaP vaccines varied by manufacturer|
|cMeningococcal C conjugate vaccine administered as part of a clinical trial at 1 MCO|
|dPneumococcal conjugate (7-valent) vaccine; some doses administered in a clinical trial at 1 MCO|
|eRotaShield® (no longer marketed)|
The number of vaccine antigens has decreased in recent years although the number of recommended vaccines has increased. The routine immunization schedule in 2013 contains more vaccines than the schedule of the late 1990s. The maximum number of vaccine antigens that a child would be exposed to today by 2 years of age is 315, compared with several thousand in the late 1990s. This is the result of changes in vaccines that allow them to more precisely stimulate the immune system. For example, the older whole-cell pertussis vaccine induced the production of approximately 3000 different antibodies, whereas the newer acellular pertussis vaccines (such as DTaP) stimulate the production of 6 or fewer different antibodies.
This study strengthens the conclusion of a 2004 comprehensive review by the Institute of Medicine of the scientific evidence that favored a rejection of the causal association between certain vaccines types and autism(3).
Knowledge, Attitudes, and Beliefs About Vaccines and Autism
Some parents are concerned that there is a link between vaccines (such as MMR) or certain vaccine ingredients (such as thimerosal) and autism. However, several large and reliable studies of MMR vaccine have been done in the United States and other countries.[3,4] None has found a link between autism and MMR vaccination. Furthermore, research does not show a link between thimerosal in vaccines and autism. Although thimerosal was taken out of childhood vaccines in 2001, autism rates have continued to climb.
Although scientific evidence shows that vaccines do not cause autism, a 2012 HealthStyles survey showed that slightly more than 15% of parents are concerned that they do (LaVail K, Fisher A, CDC; unpublished data). Data from the survey found that 22.8% of parents are concerned that children receive too many vaccines at a single doctor's visit, and 22.8% of parents are concerned that children receive too many vaccines by the age of 2 years. The vaccines, they believe, can cause learning disabilities, such as autism. In another recent survey, more than 1 in 10 parents of young children refuse or delay vaccinations in the belief that delaying vaccines is safer than giving vaccines according to the CDC-recommended immunization schedule. Children do not receive any known benefits from delaying vaccines. Delaying vaccines puts children at risk of becoming ill with vaccine-preventable diseases.
What Clinicians Can Do
CDC research with parents about their vaccine attitudes and vaccination behaviors has found that most US parents believe that vaccines are important, and they vaccinate their children. In fact, coverage for most of the routine childhood vaccines remains at or exceeds 90% in children aged 19-35 months. CDC and other agencies and organizations continue to conduct research to learn more about the causes of autism.
Healthcare professionals are the main determinants of parents' decisions about whether to vaccinate their children. This study provides evidence that clinicians can use to reassure parents that the number of vaccines received early in life is not associated with the development of autism. Clinicians can help parents to learn the signs of ASD and act early so that action can be taken to help their children reach their full potential.
Frank DeStefano, MD, MPH.
Director of the Immunization Safety Office of the Centers for Disease Control and Prevention (CDC).
DeStefano F, Price CS, Weintraub ES. Increasing exposure to antibody-stimulating proteins and polysaccharides in vaccines is not associated with risk of autism. J Pediatr. 2013 Mar 29. [Epub ahead of print]
Price CS, Thompson WW, Goodson B, et al. Prenatal and infant exposure to thimerosal from vaccines and immunoglobulins and risk of autism. Pediatrics. 2010;126:656-664.
Institute of Medicine. Immunization Safety Review: Vaccines and Autism. Washington, DC: National Academies; 2004.
Centers for Disease Control. Immunization Safety and Autism Chart.http://www.cdc.gov/vaccinesafety/00_pdf/CDCStudiesonVaccinesandAutism.pdf Accessed April 5, 2013.
Dempsey AF, Schaffer S, Singer D, Butchart A, Davis M, Freed GL. Alternative vaccination schedule preferences among parents of young children. Pediatrics. 2011;128:848-856.