Vaccine safety is one of those topics that has become so tragically mired in misinformation and myth that there can never be enough supporting evidence. So, here’s some more.

In a systematic review of the scientific literature on childhood immunizations that will be published in the August issue of Pediatrics, researchers found that vaccine-related adverse events are “extremely rare” and that — once again — the measles/mumps/rubella vaccine (MMR) is not associated with autism.

Overall, the study found that while the risks associated with childhood vaccines are not zero, the evidence shows that vaccines are “very safe” and their risks should be appropriately weighed against the health risks of the diseases they prevent. Researchers also reported “strong evidence” that the MMR, DTaP (diphtheria, tetanus and pertussis), Td (tetanus-diphtheria), Hib (immunizes against a bacteria that causes meningitis and pneumonia) and hepatitis B vaccines are not associated with childhood leukemia. The study was conducted at the request of the U.S. Agency for Healthcare Research and Quality to help identify gaps in vaccine safety evidence.

Researchers noted in the study’s introduction that while vaccines are considered one of the greatest public health achievements of the 21st century, “routine childhood vaccine uptake remains suboptimal” and that parental refusal of vaccines are contributing to disease outbreaks. For example, this year the Centers for Disease Control and Prevention is reporting a record number of measles cases, with more than 500 confirmed cases between January and July. It’s the highest caseload since measles was officially declared eliminated in the U.S. in 2000. The public health agency reports that the majority of those who’ve contracted the disease are not vaccinated.

The Pediatrics study also found moderate evidence that vaccines against rotavirus, which causes diarrhea and dehydration, can increase the risk of intussusception, a serious intestinal disorder in which one part of the intestine slides into an adjacent part of the intestine. However, the issue only occurs in one to five of every 100,000 vaccinations. Rotavirus, on the other hand, results in more than 200,000 annual emergency room visits and up to 70,000 hospitalizations. The study also confirmed earlier findings that the MMR, pneumococcal and flu vaccines are associated with febrile seizures in children, though the occurrence is “very rare.”

In a related commentary also published in the August issue of Pediatrics, author Carrie Byington, with the Department of Pediatrics at the University of Utah, pondered whether better transparency on the safety of vaccines may increase parental confidence in immunizations. Unfortunately, the jury on that topic is still very much out. She noted that a “recent report evaluating the effectiveness of messages designed to reduce parental misperceptions and increase vaccination rates, including messages about vaccine safety, demonstrated that these messages were ineffective and in some groups of parents may even reduce the intention to vaccinate.These data suggest that alternative strategies to bolster parental confidence in vaccine safety are needed.”

Byington is referencing this study published earlier this year in which parents were randomly assigned one of four different messaging interventions about vaccine safety. The interventions included explaining the lack of evidence between the MMR vaccine and autism, showing pictures of children suffering from the diseases the MMR vaccine prevents, providing information on the diseases that the MMR vaccine prevents, and offering a narrative about a child who almost died of measles. Unfortunately, none of the interventions worked to increase a parent’s intent to vaccinate his or her child. In fact, offering corrective information about vaccine safety myths actually decreased intent to vaccinate among parents with the least favorable vaccine attitudes.

Byington wrote that if parents aren’t receptive to the science, perhaps studies such as the vaccine safety literature review would be most helpful in increasing vaccine safety confidence among clinicians. In the world of vaccine messaging, it’s about the messenger, not the message. In other words, physicians may be the best conduits to relay vaccine safety information to parents.

“The relationship between parents of young children and their medical providers is powerful,” Byington wrote. “Parents trust their child’s doctor over government officials, family members or celebrities as the best source of information on vaccine safety.”

CDC estimates that vaccines will prevent more than 21 million hospitalizations and 732,000 deaths among children born in the last 20 years, saving billions of dollars in health care costs and trillions in societal costs.

For a full copy of the new vaccine study, visit Pediatrics.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.