Parents researching information about vaccinations are easily finding misinformation, despite attempts to control access to it by online platforms.
On Facebook as many as half of search results are spreading misinformation, despite the social media giant promising to crack down last year.
Otago University researchers says while most websites generated by Google and videos on YouTube were positive about vaccines (80 and 75 percent respectively), half on Facebook were negative.
Lead researcher Lucy Elkin says that's concerning, when we can see how harmful diseases like coronavirus COVID-19 are.
"People might think they're making an informed decision on whether to vaccinate their children or not, but that decision's been based on misinformation."
Dr Elkin says people may be put off vaccinating for COVID-19, when one becomes available. But in the meantime, they're not getting their kids vaccinated for preventable diseases already on the loose.
"One thing about coronavirus is that we see in the news how harmful it can be, whereas maybe we don't see that as much for things like mumps, rubella or whooping cough."
Once a person clicks on one anti-vaccine article or Facebook page, algorithms make it likely they'll see more, the researchers said.
"A person's search history is remembered and further similar content will be generated," says Dr Elkin.
"Those reading vaccine-critical information on Facebook are more likely to come across vaccine-critical information in subsequent searches on any platform, regardless of whether they are looking on social media, or on a search engine."
There is no evidence vaccines are behind autism, the most common false claim made by opponents. The doctor who first linked vaccines with autism was later outed as a fraud and banned from practising.
Diseases like measles and chickenpox struggle to spread when most of the population has been vaccinated - this 'herd immunity' protects babies and those unable to have the vaccine for medical reasons.
A Facebook company spokesperson says it works hard to reduce the spread of vaccine misinformation on its platforms, and show credible sources to give people accurate information.
It says it's committed to working with external health experts like the World Health Organization, which has publicly identified verifiable vaccine hoaxes; and if these vaccine hoaxes appear on Facebook's platforms it will take action against.