(NaturalNews) In a study published in the, medical researchers warn that anti-vaccination activists are using YouTube to get their message across and say that pro-vaccination forces need to respond in kind with an ensuing media campaign.Researchers Kumanan Wilson and Jennifer Keelan of the University of Toronto did a search on YouTube for the terms "vaccination" or "immunization" in February 2007 and analyzed the videos based on how they presented vaccinations. In all, 73 portrayed immunization positively, 49 negatively and 31 were classified as "ambiguous." Forty-five percent contained messages contradicting Canadian or U.S. vaccination recommendations.The study and subsequent press release concluded that medical professionals need to respond to this use of YouTube."Health care professionals need to be aware that individuals critical of immunization are using YouTube to communicate their viewpoints and that patients may be obtaining information from these videos," Wilson said. "The findings also indicate that public health officials should consider how to effectively communicate their viewpoints through Internet video portals."Also troubling to the researchers was the finding that videos critical of vaccinations were viewed more often and ranked higher by YouTube users than pro-vaccination videos."Other people ... just from the view counts and the ratings, are coming on and wanting to find out more about these viewpoints," Wilson said.Among the videos posted were recordings of parents saying their children's autism had been caused by specific vaccines or by the vaccine ingredient thimerosal, which contains mercury."[YouTube is] the perfect venue for an anecdote, both positive or negative," Keelan said. Wilson said that vaccine advocates can no longer ignore or marginalize anti-vaccine advocates."In the past that could work, but it's not going to work anymore. Now there are ways for people with these viewpoints to communicate with each other," he said. "These sites are now providing people with a mechanism by which they can bypass the conventional filters and get their messages out. It can be dangerous.""In other words," said consumer health advocate Mike Adams, "the conventional medical industry views free speech communication as a dangerous thing. They don't want people to exercise their free speech rights about vaccines: They want all words, information and even thoughts to be approved by a central controlling authority that denies any link between vaccines and autism."