Doubts about vaccines have spread across social media like a disease and false information that “kills people” should be taken down by the companies running digital platforms, the head of global vaccine alliance Gavi said on Tuesday.

Speaking at a U.S.-sponsored event on the sidelines of the World Health Organization’s annual assembly in Geneva, Gavi CEO Seth Berkley said there was a strong scientific consensus about the safety of vaccines.

But social media algorithms favored sensational content over scientific facts, rapidly convincing people who had never seen family members die from preventable illness.

“We have to think about it as a disease. This is a disease,” Berkley said. “This spreads at the speed of light, literally.”

WHO says poor vaccination coverage is causing measles outbreaks globally, with numbers spiking in countries that were previously almost free of the disease, including the United States.

Misinformation about vaccines, which the WHO says save two million lives annually, was not a freedom of speech issue and social media firms need to take it offline, Berkley said. “I remind people that this kills people,” he said.

U.S. Health and Human Services Secretary Alex Azar said complacency, misunderstanding and misinformation were causing vaccination rates to decline globally, with tragic results.

“In my country, social media conspiracy groups confuse well-meaning parents so they hesitate to get the recommended vaccinations,” Azar said.

He rejected any criticism of U.S. President Donald Trump, who repeatedly and erroneously tweeted about links between vaccines and autism in the years before he became president.

“A study says @Autism is out of control — a 78% increase in 10 years. Stop giving monstrous combined vaccinations,” Trump tweeted in 2012.

Azar said Trump was “extremely firm” in support of vaccination.

“If you had been paying attention in the last month, you would know that the President of the United States, President Trump, was very clear and emphatic: get your shots, get your kids vaccinated, vaccines are safe,” Azar said.

Canada’s Chief Public Health Officer Theresa Tam said health authorities needed to “up our game,” adding that she was working with Twitter, Facebook, Google and other tech companies.

“You’ve got to get into the trenches … and begin to get engaged much more on a personal and emotional level, because people don’t understand statistics and data. If you do that
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