But who read the tweet? Ms Hughes runs the Immunisation Foundation of Australia. Nearly all of her followers are fellow vaccine advocates, she says. She may have been preaching to the choir. “To be honest,” Ms Hughes says, “the people I follow are the people who support vaccinations. And the people who follow me, I think they are all pro vaccination. We create these echo chambers.” Humans naturally seek opinions that agree with their own. It’s called confirmation bias. On Twitter, it manifests with users tending to follow accounts that tweet messages they already agree with.

Immunisation coverage rates for children are close to 95 per cent. Credit:Shutterstock That’s a big problem if you want to use Twitter to change someone's mind. “The people you want to listen,” says Professor Mark Alfano, “aren’t the ones who are listening.” Professor Alfano has spent the last few years studying pro and anti-vaccination accounts on Twitter. For people like Ms Hughes, his findings are depressing. “The people who are sceptical of vaccines, they basically only talk to each other,” he says. “And the people who are in favour of vaccines, they only talk to each other.”

His Australian Catholic University team looked at hundreds of thousands of tweets from Australian pro and anti-vax Twitter accounts sent in March 2018. Both sides frantically argued their case. But the networks never overlapped. They were living inside their own filtered conversations. Professor Alfano, however, has a cunning plan to pop those bubbles. He plans to find people who are influential in the anti-vax community, but who seem at least a little open-minded.

Then he will try to change their minds. More than a million dollars has been secured to run an influence campaign. The funding comes from the federal government and the Templeton Foundation, a huge philanthropic trust with links to conservative and religious politics. The team plans to build an algorithm that can work out the best messages to send and when to send them. Pro-vax tweeters will be told the best accounts to target, and the best messages to use. Targeted adverts will be purchased. All the messages will be tuned to convey trustworthiness and compassion.

“The messages that seem to resonate most are not ones that invoke hard evidence,” Professor Alfano says. “They are the ones that convey a sense of trustworthiness. That doctors and scientists and drug manufacturers have people’s best interests at heart.” If he can turn these users, they will hopefully start spreading pro-vaccination messages to their friends and followers – who already trust them. But is this a good idea? Other experts on ‘vaccine hesitancy’, as it is known, praised the initiative but were sceptical of its chance of success. Arguing with someone often causes them to become more entrenched in their views, not less – a phenomenon known as the ‘worldview backfire effect’.

“They don’t feel they are being heard," says Professor Julie Leask, a University of Sydney behavioural scientist. “And they can learn to articulate their own arguments more clearly in their own minds. This is the real challenge we have in addressing anti-vax sentiment.” Professor Leask also questioned the wisdom of spelling out the infiltration strategy in the media before its launch. It may be the case that true anti-vaxxers aren’t ever going to be convinced to change their mind. But this is not the end of the world, argues Professor Leask. Immunisation coverage rates for children are close to 95 per cent. “The anti-vax movement is like a wasp’s nest," she said. “They’ve been there since the development of the first vaccine. And sometimes poking a stick at them can cause their messages to spread further.