Parents have yet one more reason to vaccinate their children: Routine immunizations may reduce the risk of childhood stroke, according to a new study.
Childhood strokes are rare, estimated to affect between three and 13 children per 100,000. Yet unlike adult strokes, in which environmental factors such as smoking and poor nutrition play a major role, susceptibility to childhood strokes is largely genetic. And parents often don't know if their child is at risk.
The new study, led by Dr. Heather Fullerton of University of California, San Francisco, confirmed previous findings that minor infections may trigger acute ischemic strokes in children who are at risk. Ischemic strokes involve a blockage in a blood vessel in or near the brain.
The researchers compared 355 children who had had ischemic strokes with 354 children who had not. The scientists found that children with an infection had six times the risk of experiencing a stroke within that week; 18 percent of children who experienced strokes had such an infection, according to the findings, published today (Sept. 30) in the journal Neurology. [9 Weird Ways Kids Can Get Hurt]
Fullerton and her colleagues also found that children who were up to date on their immunizations had a far lower risk of experiencing a stroke. Under-vaccinated children (those who were not up to date on their vaccinations) were up to seven times more likely to have a stroke compared with children who had all or most of their immunizations.
The reason for the apparent link between vaccinations and stroke is not clear, Fullerton told Live Science. Vaccines clearly prevent major infections, such as those caused by chickenpox, measles and tetanus. It could be that vaccines reduce a child's overall lifetime infection burden, and prevent the subsequent damage that infections and inflammation have on blood vessels, she said.
Fullerton added that parents who keep their children up to date on immunization may be more proactive about their child's health care in general, compared with parents who don't vaccinate. So this might also explain the link seen with vaccines, she said.
The study has ruled out two "lingering doubts" that some have had about infections and strokes, Fullerton said. One was the worry that vaccines themselves could trigger a stroke, which is biologically plausible given that vaccines are a form of controlled infection. But the study found the opposite, offering more evidence that "all kids should get vaccinated," Fullerton said.
Another worry was that a seeming link between infections and strokes was actually due to cold medications such as vasoconstrictors. These medicines reduce swelling and congestion by constricting blood vessels, and it was thought that perhaps the drugs could trigger strokes. However, Fullerton said, the study found no evidence to support this.
The findings will be "seminal in drafting further stroke-prevention strategies" in children, wrote Dr. Jose Biller of Loyola University Medical Center in Chicago and Dr. Geoffrey Heyer of The Ohio State University in Columbus, Ohio, in an accompanying editorial in Neurology. Biller and Heyer were not associated with the study.
"Oftentimes parents and even physicians may not be aware — [it's] not on their radar screen — that strokes may affect neonates, toddlers and children," Biller told Live Science. "Education is key," he said. Many children who have strokes often suffer from the health effects of the stroke for their whole lives, and so preventing strokes is very important.
Fullerton said that more than half of childhood acute ischemic strokes happen to children who are seemingly healthy, so the stroke comes as a surprise. Conditions that increase stroke risk in children include congenital heart disease, sickle cell disease and lupus, she said. There is no reason why children with these conditions should avoid vaccination, she said.
The research effort was part of a large, international case-control study of childhood stroke, called the Vascular Effects of Infection in Pediatric Stroke (VIPS) study. The study authors represent more than a dozen universities and institutions worldwide. Fullerton said the research offers an "avenue for understanding what's going on" with childhood strokes.
Many questions remain, such as why infections can trigger a stroke in seemingly healthy children, but there is at least one take-home message from this research, Fullerton said: "This is another example of a pretty morbid disease that vaccines can help prevent."
Biller said that vaccines appear to offer a lifetime of cardiovascular benefits. A study published in 2013 in the Journal of the American Medical Association found that for adults who get the flu shot, the odds of having a stroke, heart attack or other major cardiac event are lowered by about a third lower over the following year. Biller said that some studies have shown that getting the flu shot yearly provides even greater protection.
"Vaccines are among the safest medical products," Biller said. "The safety and effectiveness of vaccines routinely given to children and adults has been overwhelmingly favorable."
Follow Christopher Wanjek @wanjek for daily tweets on health and science with a humorous edge. Wanjek is the author of "Food at Work" and "Bad Medicine." His column, "Bad Medicine," appears regularly on Live Science.