Holly Ann Haley gets vaccinations last year at the doctor's office in Berlin, Vt. Another study finds no connection between vaccines and autism.
(Photo: Toby Talbot, AP)
(USA TODAY) -- At least 10% of parents of young children skip or delay routine vaccinations, often out of concern that kids are getting "too many shots, too soon."
A new study finds that children who receive the full schedule of vaccinations have no increased risk of autism.
"This is a very important and reassuring study," says Geraldine Dawson, chief science officer at Autism Speaks, who wasn't involved in the new paper. "This study shows definitively that there is no connection between the number of vaccines that children receive in childhood, or the number of vaccines that children receive in one day, and autism."
The study, published today in the Journal of Pediatrics, is the latest of more than 20 studies showing no connection between autism and vaccines, given either individually or as part of the standard schedule. The paper is the first to consider not just the number of vaccines, but a child's total exposure to the substances inside vaccines that trigger an immune response.
Study authors say they sought to address the fear that multiple vaccines are "overwhelming" children's immune system, possibly contributing to long-term problems. Twenty years ago, children were vaccinated against nine diseases. Today, they're vaccinated against 14, according to the Centers for Disease Control and Prevention, which funded the study.
Though kids get more needle sticks, the next-generation vaccines they receive are easier on the immune system than those used two decades ago, says Frank DeStefano, lead author of the new paper and director of the Immunization Safety Office at the Centers for Disease Control and Prevention.
That's because modern vaccines are more sophisticated, using just a few critical particles - called antigens - to stimulate the immune system, DeStefano says. These antigens, found on the surfaces of bacteria and viruses, spur the body to make antibodies, which block future infections.
For example, an older version of the pertussis (whooping cough) vaccine, used until the late 1990s, was made using an entire, killed bacteria. That vaccine, called DTP, exposed the body to more than 3,000 antigens.
A newer, streamlined version, called DtaP, uses only the four to six antigens critical to producing immunity, DeStefano says.
Because of these sorts of improvements, fully vaccinated 2-year-olds are exposed to a total of 315 antigens, the study says.
That's a drop in the bucket compared with the billions of microbes - from bacteria to yeast - that babies encounter in their first hours of life.
The new research confirms the findings of a 2010 study in Pediatrics, which compared babies who received all vaccines on time in the first year of life with those who skipped or delayed their shot. That research found no neuropsychological differences, such as stuttering, facial tics or lower scores on IQ tests.
"A lot of parents are concerned about the number of 'owies' that children get," says Michael Smith, an author of the 2010 study and pediatric infectious disease specialist at the University of Louisville School of Medicine.
"But there's no benefit to delaying vaccines," says Smith, who wasn't involved in the new study. "When you delay your child's vaccines, you put them at risk."
STORY: Why don't teens get shots for HPV and other diseases?
Myths about autism and vaccines have persisted, in spite of the scientific evidence, partly because researchers don't really know what causes autism, Dawson says. "Until we conduct the research to answer the questions about autism's causes and risk factors, parents will continue to have questions," she says.
Research increasingly suggests that many of the underlying changes that cause autism take place before birth, and even before conception. Although parents often notice symptoms of autism only after a child is 12 to 18 months old, research by Dawson and others picked up subtle changes - in eye gaze or even brain patterns - as early as 6 months.
Doubts about vaccines have led to low vaccination rates in some communities, which have fueled flare-ups of once-forgotten diseases such as whooping cough, measles and mumps, Smith says. "If someone gets on a plane from Europe or India where there is measles, then we have measles again," Smith says.
The CDC reported Thursday that the USA had three cases last year of congenital rubella syndrome, an often fatal condition that afflicts the newborns of mothers who contract rubella, or German measles, while pregnant. Affected babies often suffer from a number of painful and life-threatening problems, such as heart defects, deafness, cataracts and mental retardation.
Vaccination has eliminated person-to-person spread of rubella in the Western Hemisphere. All three of the mothers last year were from Africa, where rubella still circulates. One of the babies died.
Though some parents may never believe vaccines are safe, the new study will probably reassure many others, says Karen Ernst of Voices for Vaccines, a group of parents and other vaccine advocates.
"Those who truly benefit from this article are the children of future parents," Ernst says. "These future parents will have more confidence in vaccinating their children on time. It is the job of parent-advocates like our members to speak up and make sure news about articles like this gets out."