The health of Kiwis is being harmed by social media and fake news, a medical expert says.

The safety of vaccinations, the reality of the obesity epidemic and the potential benefits of a sugary drink tax have all come under fire thanks to populist leaders and fake news despite the wealth of scientific evidence behind them, the immediate past president of the World Federation of Public Health Associations, Professor Michael Moore, said.

Moore was among the speakers who addressed the Royal Australasian College of Physicians in Auckland this week about the rapid spread of popular perceptions which harmed public health - made largely possible by social media.

The most prolific problem were the populist attacks on vaccinations which were not backed by scientific evidence and could discourage people from getting them, he said.

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His warning came in the same week Education Minister Chris Hipkins labelled parents who did not vaccinate their children "pro-plague".

Hipkins' comments followed news of two cases of measles in Northland and calls from the region's district health board for schools to consider sending unvaccinated children home for at least two weeks.

The move could affect about one in every six Northland schoolchildren.

Prime Minister Jacinda Ardern also waded into the fray saying false information that vaccinations were not safe was damaging.

While concerns about vaccinations first reared its head in the 1990s, thanks to a now discredited study, a global rise in the number of measles cases this year has been blamed on the spread of the anti-vaccination message by influencers and social media.

In March, Facebook took steps to combat the issue announcing it would reject ads containing misinformation about vaccinations and make sure pages and groups that spread misinformation would not appear in searches and recommendations and will be lower ranked on people's newsfeeds.

Speaking to the Herald this week, Moore said it was a world-wide issue and the importance of vaccinations was not the only public health message to be regularly targeted by fake news and popularist leaders.

He said there had been a major resistance to suggestion of a sugary drinks tax in Australia despite the benefits seen in Mexico where it had been introduced.

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The number of jobs that would be lost and the impact on the economy if such a tax was introduced had been significantly exaggerated, he said.

Moore said the debate around unhealthy food and obesity-related deaths, and the social determinants of health faced the same hurdles.

"It's really hard when the populist media is blaming the victims."

Perhaps less harmful, but equally prolific were the run of fad diets pushed by influencers, Moore said.

"They have had huge interest with no evidence behind them whatsoever."

Moore believed physicians could play an important part in battling the relatively new issue.

He encouraged them to use their respected standing in the community to band together, to develop influential relationships, speak out against misinformation and push for change.