It goes without saying that, in the eyes of their parents, children are unimaginably important, precious, and at times vulnerable. And any parents who are concerned about the possible effects of vaccines have their hearts in the right place when they try to seek out relevant medical information on the Internet.

Unfortunately, as many of us are aware, the web is not necessarily a great place to do this kind of research, and now a broad study of anti-vaccination websites helps to explain why. Researchers from the Johns Hopkins University Bloomberg School of Public Health analysed close to 500 anti-vaccination websites and found that they deliver a distorted mixture of pseudoscience and misinformation to parents seeking information about vaccines.

According to the researchers, more than two thirds of anti-vaccination websites present non-scientific information and other forms of misinformation as 'scientific evidence' to support the view that vaccines are dangerous to children, and nearly one third of sites reinforce the idea through the use of anecdotes and stories.

The researchers used search engines including Google, Bing, Yahoo and Ask Jeeves to find the sites, using search terms like "immunisation dangers" and "vaccine danger" to see where it led them.

The study found that the resulting mix of blogs, personal websites, Facebook pages and health sites perpetuate an alarming mixture of misinformation about vaccines and use a range of persuasive techniques to get the reader on side.

Almost two thirds of the sites suggested that vaccines cause autism, and more than 40 percent claim they're responsible for 'brain injury'. The majority present information as scientific when it doesn't actually qualify for that distinction.

In addition to condemning vaccines, the sites also promote some positive behaviours, such as healthy eating (recommended by 18.5 percent of anti-vaccination sites), and the benefits of breastfeeding (5.5 percent) and eating organic food (5.2 percent).

The study, presented this week at the American Public Health Association's annual meeting in Chicago, may help actual scientists – such as doctors and health care workers – better understand how to reach and communicate with parents who are genuinely concerned about any perceived risks of vaccination (and who may be exposing themselves to potentially dangerous misinformation on these kinds of sites).

"The biggest global takeaway is that we need to communicate to the vaccine-hesitant parent in a way that resonates with them and is sensitive to their concerns," said Meghan Moran, an associate professor in the Bloomberg School's department of health, behaviour and society.

"In our review, we saw communication for things we consider healthy, such as breastfeeding, eating organic, the types of behaviour public health officials want to encourage. I think we can leverage these good things and reframe our communication in a way that makes sense to those parents resisting vaccines for their children."