In 2005, a combination vaccine called Tdap was introduced to protect against tetanus, diphtheria and pertussis. By 2013 the CDC began recommending the vaccine for all pregnant women as evidence suggested it effectively conferred immunity to the child. A large study from researchers at Kaiser Permanente has now shown prenatal Tdap vaccinations do not in any way increase a child's risk for developing autism, adding even further weight to the massive body of scientific evidence refuting this modern misconception.

Pertussis is commonly known as whooping cough, and in the early 20th century it was known to devastatingly affect hundreds of thousands of children every year. Following the development of an effective vaccine in the 1940s infections rapidly declined, until debates over the safety of the vaccine arose in the 1980s. Since then, reported cases have continually increased with several small epidemics declared in the United States over the past decade.

Vaccines protecting against pertussis have continually improved in safety and efficacy over recent years, and studies have effectively shown the newer Tdap vaccination to be especially beneficial when mothers are immunized during pregnancy. This latest study set out to scientifically clarify whether there was any link between prenatal Tdap vaccination and autism, considering the recommended administration protocol was relatively new.

"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," says Hung Fu Tseng, senior author on the new research. "We hope that our findings reassure parents that Tdap vaccination during pregnancy was not associated with autism in children."

The study examined 81,993 children born over a four year period between 2011 and 2014. Children born from mothers vaccinated with Tdap during pregnancy displayed autism spectrum disorder incidence rates of just 1.5 percent, compared to autism rates of 1.8 percent in the unvaccinated group. Generally, diagnosed autism rates in the United States sit around the 1.7 percent mark.

The results confidently conclude that Tdap prenatal vaccinations do not correlate with any identifiable increase in autism risk. Tracey Becerra-Culqui, lead author on the new research, suggests the waning immunization rates against pertussis in the United States affirm the importance of mothers getting vaccinated during pregnancy.

"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," says Becerra-Culqui.

The new research was published in the journal JAMA Pediatrics.