The pro-vaccination sign written by an Australian doctor going viral worldwide.

Sunni Mariah was at her doctor’s office in Colorado when she noticed a sign up on the wall, promoting vaccination. So she took a photo and posted it on Facebook, commenting that the sign was “throwing some serious shade”.

Within a few days, the post had been shared more than 130,000 times, and had sent anti-vaxxers into a fury. What Mariah didn’t know was that the words on the sign had been written by a doctor from Australia, Rachel Heap.

Dr Heap is an intensive care specialist who works in the Northern Rivers region of NSW. In her spare time, she politely and respectfully does her best to correct misinformation put out by “professional anti-vaxxers”. It’s tough work, but she keeps at it.

“The ghosts of the people that I’ve looked after keep driving me,” she tells Mamamia.

Those “ghosts” are her patients who have died, or suffered horribly, from vaccine-preventable diseases.

In a six-month stint working in a kids’ intensive care unit, Dr Heap looked after babies with whooping cough. Two stick in her memory. There was one baby who spent six months in intensive care, and may have been left with permanent brain damage.

“The other one didn’t make it,” she says sadly.

“Those are two of my ghosts, but I’ve got countless, endless other ones, because people don’t count the adults. The 28-year-old guy who died of late complications of whooping cough. The people who’ve died of influenza – young, healthy people as well as the older and more frail. Name a vaccine-preventable disease, other than polio, and I’ve seen it directly.

“How can I not continue this fight? And no, I’m not paid for it. Most of the people in the pro-vax field, we do this in our spare time, because we are passionate about protecting the vulnerable.”

Dr Heap, who is one of the founders of the Northern Rivers Vaccination Supporters, wrote the words on the sign about two years ago. At the time there was a lot of debate about the “no jab no pay” policy.

“I kept hearing loads of comments about the parent’s right to choose and stuff like that, almost like the kids were possessions,” she remembers. “To me, it’s all about the rights of the child. These diseases can impact on their whole lives.

“You don’t get to choose whether your kid wears a seat belt. There’s stuff in place to protect children. You don’t own your children. That upset me.”

Dr Heap had just come off a “pretty tough spell” in the intensive care unit.

“We look after people dying of influenza. I’ve looked after people with complications of cervical cancer. We looked after a guy with mumps. The two things kind of hit together. I did a rant, from the heart. It’s the truth as I experience it, as I live it, every day.”

In the rant, Dr Heap wrote that not vaccinating children can leave them vulnerable to disease their whole lives.

“When your daughter gets rubella when pregnant, how are you going to explain that you chose to leave her at risk?

“What will you say when she calls you and tells you she has cervical cancer, because you decided that she wouldn’t need the HPV vaccine?

“What do you tell your son when he breaks the news to you that he cannot have kids, thanks to the mumps that he got as a teenager?

“And what do you say when he gives influenza to his grandma? How do you explain that she won’t be coming home from hospital? Not ever.

“Do you tell them that you didn’t think these diseases were that serious? That you thought your organic, home-cooked food was enough to protect them?

“Do you say sorry?”

She posted her rant online, and pretty much forgot about it. A nurse from Colorado contacted her to see if it was okay to print it out and put it up in their doctors’ office. It was from there that it went viral.

Prime Minister Malcolm Turnbull on why the Australian Government is 100 per cent behind vaccination. Post continues.

Dr Heap admits that the tone of her words is a bit different to the “polite and respectful” tone generally used by the Northern Rivers Vaccination Supporters. Their approach is to help educate people so they can make informed choices.

“I don’t usually ‘throw shade’ – that’s not really what we do – but once in a blue moon, the emotion gets to us.”

Dr Heap and the rest of the Northern Rivers Vaccination Supporters are going to keep working away, in their spare time, to correct misinformation about vaccines. That involves “trawling through crap” online. It also involves talking to friends and neighbours – an approach that they call “one thousand cups of tea”.

“We live here. This is our community. These are our friends. I don’t want to see the neighbours’ kids come down with measles. I don’t want to look after people in ICU that I know. So we keep going.”