But every now and then, a tweet cuts through the miasma. Like the message from a father who had decided not to vaccinate his daughter.

"He said something I tweeted changed his mind," said Associate Professor Leask at the University of Sydney's School of Public Health.

She asked him what she had tweeted. Surprisingly it was an Institute of Medicine report. A dense, technical document of hundreds of pages that outlined vaccine risks.

"He needed that. He needed to see the risks associated with vaccines was being looked at in this intense detail," said the internationally renowned public health expert specialising in immunisation controversies, vaccination.

Twitter is a melting pot of vaccination information, misinformation, vitriol and support with clear, deeply polarised feedback loops where staunch anti-vaccination proponents consume a social media diet of like-minded views, in the same way vaccine advocates are largely exposed to pro-vaccination messages.

The social media quagmire is also more accurate than socio-economic census data at mapping vaccination rates across vast communities, an Australian and US study has shown.

The research team used Twitter the way meteorologists use rain gauges to determine rainfall over sprawling geographical expanses.

"Instead of catching rain we catch tweets," said lead author Dr Adam Dunn at Macquarie University's Australian Institute of Health Innovation.

Trawling through more than 250,000 tweets about the HPV vaccination globally between October 2013 and October 2015, the researchers localised over 34 million US Twitter users to their state or county using information in their Twitter profiles.

They monitored users' exposures to positive and negative information about the HPV vaccine on Twitter (up to 291.8 million exposures in total), including misinformation, conspiracies and scare tactics to gauge the broader media diets.

Vaccine coverage was lower in states and counties where users were exposed to higher proportions of tweets dealing with safety concerns, misinformation and conspiracies, concluded the study published in the journal Vaccine.

For instance, a series of anti-vaccination content on the Katie Couric show, in which she prominently featured anti-vaccination campaigners including celebrity Jenna McCarthy, Dr Dunn said.

People who were exposed to tweets and webpages linked to the show were more likely to be in states that had lower vaccination rates.

"We're not saying that Katie Couric caused lower vaccine coverage. What we're saying is that there was an association between people exposed to this and low vaccination rates," he said.

The social media platform could prove a faster, cheaper tool for governments spending tens of thousands of costly community surveys to identify areas with high rates of vaccine hesitancy or refusal, and the possible reasons at play, the researchers suggested.

And Australia likely follows a similar pattern, said Dr Dunn who is planning to use the same method to map Australian vaccine coverage.

"The types of arguments people have in the US about vaccination are very similar to the conversations we have in Australia and we have the same clustering of vaccine refusal here as they do in the states," he said.

Brunswick Heads on the NSW North Coast has the lowest rate of immunisation in Australia (73.3 per cent of one-year-olds are immunised), followed by Parramatta and Harris Park, according to the most recent data from the AIHW.

It is unclear whether decisions people made about vaccination were influenced by their exposure to certain tweets and media, or whether they simply chose to inhabit an online community that reinforced their beliefs, a tension known as contagion versus homophily.

They feed into each other, said Professor Leask, a co-author of the study. She believed social media generally reinforced existing sentiments in the community, but there was some wiggle room.

Health professionals and advocates of vaccination appear to be engaging a lot more on social media.

"Generally speaking this is a really good thing because we don't want parents to raise unfounded concerns about vaccination in a vacuum," Professor Leask said.

"If there is a void the anti-vaccination advocates will opportunistically jump in.

"As professionals we need to be engaged in those spaces, but how we engage is really important."

Though there were two competing schools of thought that informed how they interact.

Some vaccine advocates expose, even vilify the anti-vaccination movement in an effort to call them to account on social media.

But this tactic can backfire, drawing more attention to anti-vaccination messages, Professor Leask said.

The alternative involves ignoring the hardline activists and vaccine refusers, and instead engaging with the fence sitters.

"Talk to parents who are hesitant about vaccination but not entrenched in their decision and certainly not an anti-vaccination advocate," Professor Leask said.

"We need to listen and validate their concern for their children as parents and reasonably and calmly address the issues they raise.

"Anger and vitriol and attempts to shout louder across the divide may disengage these important audiences."