Vaccines and Autism: CDC Study Says No Connection

New CDC Study of Vaccine Doses and Autism

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	Doses^a
Diphtheria toxoid/tetanus-diphtheria (DT/TD)	2	14
Diphtheria-tetanus-pertussis (DTP)	3002	235
DTP - Haemophilus influenzae type B (Hib)	3004	1659
Diphtheria-tetanus-acellular pertussis (DTaP)	4^b	1165
DTaP	5^b	789
DTaP	6^b	492
DTaPHepatitis B	6^b	3
Influenza	10	95
Hib	2	2123
Hepatitis A	4	22
Hepatitis B	1	3085
HepatitisB-Hib	3	215
Measles, mumps, rubella (MMR)	24	1093
Measles	10	2
Meningococcus^c	2	285
Mumps	9	1
Pneumococcus^d	8	698
Polio	15	3385
Rabies	5	1
Rotavirus^e	14	57
Rubella	5	2
Typhoid	3000	4
Varicella	69	917
Yellow fever	11	1

^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]