A Kaiser Permanente study of more than 80,000 children born over a 4-year period showed that the prenatal Tdap vaccination (tetanus, diphtheria, acellular pertussis) was not associated with increased risk of autism spectrum disorder in children. The study was published today in Pediatrics.

"Infants are at the highest risk of hospitalization and death among any population subgroup after contracting a pertussis infection, a highly contagious respiratory disease also known as the whooping cough," said Tracy A. Becerra-Culqui, PhD, a post-doctoral research fellow with Kaiser Permanente Southern California's Department of Research & Evaluation and lead author of the study. "With waning immunity against pertussis in the United States, it has become very important for pregnant women to be immunized against pertussis. It is an immunity they pass on to their unborn baby."

"Pregnant women can be reassured by this study that there is no indication of an increased risk of autism spectrum disorder in children after being exposed prenatally to the Tdap vaccine," Becerra-Culqui added.

The Advisory Committee on Immunization Practices, which provides guidance on the use of vaccines for the United States, recommends pregnant women receive the Tdap vaccine to prevent pertussis infection, but some women still hesitate.

Kaiser Permanente researchers were able to comprehensively study the hypothesized link between Tdap and autism because of the organization's large and diverse patient population. In Southern California, Kaiser Permanente provides health care in 15 hospitals and about 220 medical offices to approximately 4.4 million members who are broadly representative of the area's population. Recommended vaccinations are free to all members.

This retrospective cohort study looked at the autism diagnosis for children born at Kaiser Permanente hospitals in Southern California between Jan. 1, 2011 and Dec. 31, 2014.

The study included 81,993 children and found that:

Prenatal Tdap vaccination coverage ranged from 26 percent for the 2012 birth cohort to 79 percent for the 2014 birth cohort.

The autism spectrum disorder incidence rate in children was 1.5 percent in the maternal Tdap vaccinated group and 1.8 percent in the maternal unvaccinated group, comparable to autism rates in the United States (1.7 percent).

Analyses of the data extracted from electronic health records showed that Tdap vaccination during pregnancy was not associated with increased autism spectrum disorder risk in children.

Results were consistent across study birth years and among first-born children.

"The link between vaccination and development of autism has been refuted by many rigorous scientific investigations. Unfortunately, the misconceptions still generate concerns," said the paper's senior author, Hung Fu Tseng, PhD, of the Department of Research & Evaluation.

"Given the increasing practice to vaccinate pregnant women with Tdap vaccine, it was important to address the concern of a link between maternal vaccination and subsequent development of autism spectrum disorder in children," he added. "We hope that our findings reassure parents that Tdap vaccination during pregnancy was not associated with autism in children."

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Other authors on this study include Darios Getahun, MD, PhD, Vicki Chiu, MS, and Lina Sy, MPH, all of the Kaiser Permanente Southern California Department of Research & Evaluation.

This study was supported by Kaiser Permanente Southern California internal research funds.

About the Kaiser Permanente Southern California Department of Research & Evaluation

The Department of Research & Evaluation conducts high-quality, innovative research into disease etiology, prevention, treatment and care delivery. Investigators conduct epidemiologic research, health services research, biostatistics research, and behavioral research as well as clinical trials. Major areas of study include chronic disease, infectious disease, cancer, drug safety and effectiveness, and maternal and child health. Headquartered in Pasadena, California, the department focuses on translating research to practice quickly to benefit the health and lives of Kaiser Permanente Southern California members and the general public. Visit kp.org/research.

About Kaiser Permanente

Kaiser Permanente is committed to helping shape the future of health care. We are recognized as one of America's leading health care providers and not-for-profit health plans. Founded in 1945, Kaiser Permanente has a mission to provide high-quality, affordable health care services and to improve the health of our members and the communities we serve. We currently serve more than 12.2 million members in eight states and the District of Columbia. Care for members and patients is focused on their total health and guided by their personal Permanente Medical Group physicians, specialists and team of caregivers. Our expert and caring medical teams are empowered and supported by industry-leading technology advances and tools for health promotion, disease prevention, state-of-the-art care delivery and world-class chronic disease management. Kaiser Permanente is dedicated to care innovations, clinical research, health education and the support of community health. For more information, go to: kp.org/share.