Eight in 10 Australians carry the virus that killed Jack. This is what his mum wants you to know.

After six nights in hospital, her c-section wound healing, Jess Buchanan was preparing to take her newborn son, Jack, home for the first time.

“I remember looking at my bub in his capsule, he looked a bit different. I said to [my husband] Angus, ‘Does he look okay to you?’

“‘Yep, let’s go,’ he replied, and I didn’t give it another thought.

“We went home.”

Just a few days later little Jack died, his future robbed by a virus roughly 80 per cent of the Australian population carry: Herpes Simplex 1, commonly known as the cold sore virus.

Sharing her story to Dad Minus One, the blog of vaccination campaigner and Light For Riley co-founder Greg Hughes, the mother recounted the final days of Jack’s cruelly short life; from the restlessness, the reluctance to take the bottle, to the the dry nappies during his second night at home.

By the third morning, the couple were racing back to the hospital. A specialist team spent five and a half hours attempting to stabilise the newborn, before he was transferred to Sydney Children’s Hospital.

"When we went into an isolated room in ICU I knew things were really bad. They hooked Jack up to every medication you could imagine. He had drips in his feet. They couldn’t regulate his body temperature," Jess wrote. "The hours that followed were harrowing. There was nothing we could do to help, just watch as the doctors and nurses did their thing."

Despite their best efforts, Jack died at 10:10am on Monday, Sep 21, 2015.

"I remember asking the ICU doctor to stop CPR," Jess wrote. "They unhooked Jack and placed him in my arms. The noise that came out of my mouth is something that is almost indescribable. It was the sound of pure pain."

Why are cold sores dangerous for babies?

While eight in ten people carry the HSV-1 virus, only 30 per cent actually present physical symptoms in the form of cold sores. And it's those people who pose a risk for newborns.

These sores, which generally last between seven to 10 days, can be highly contagious and potential deadly for babies under four weeks old, as their immune systems haven't fully developed. As ACT Health notes, symptoms can include tiredness, irritability, poor feeding, and don't always involve obvious blisters or ulcers.

Still, contraction of either HSV-1 or its genital counterpart HSV-2 is rare among newborns. According to the Victorian Government's health hub, infection occurs in less than five of every 100,000 births.

The vast majority of these are passed from mother to baby during the birthing process. In fact, infection has been contracted after birth in just five per cent of newborn cases, according to Vic Health.

When it does, it's the result of direct physical contact. As the Federal Government's Health Direct portal explains this may include kissing, skin to skin contact, sharing drink containers or eating utensils, towels or toothbrushes.

It's important to note that transmission of HSV-1 can occur even when a blister isn't present, as people with a history of cold sores may shed the virus in their saliva.

As Jess wrote, "Did Jack catch it off a nurse? Did he catch it off me? ‘You can send yourself mad trying to figure it out,’ the head of ICU said.

"When I’ve told Jack’s story to people and followed with, ‘It’s a good idea not to kiss your baby’, they look at me like I’m mad," she added. "Kissing a baby is the most natural thing in the world."

Baby Jack's legacy.

In the wake of Jack's death, Jess's eldest son, Aiden, has helped keep her and Angus going.

"I don’t know where I would’ve been without my oldest boy. He made us laugh when there was nothing the laugh about. He distracted us with love when things were just so bad," she wrote. "Had I had no other children, I probably would’ve gone to bed never to emerge again. It doesn’t surprise me that 70 per cent of couples who lose a child where they have no other children end up divorcing."

But the tragedy took a toll on the toddler, too. After his little sister came into the world one year and three days later, he had questions.

"Aiden was three and a half years old and kept asking if Eloise was going to die like Baby Jack," she said. "Such overwhelming conversations to have with a child so young."

Sparing other families, other parents, other big brothers from this grief is precisely why Jess has chosen to write about Jack.

"If me telling his story encourages just one person to wash their hands extra well, to take extra precautions around babies or to avoid contact completely if they feel the tingle of a cold sore on their lips," she wrote, "then it will have been worth it."