Finally home after a bone marrow transplant in March, Chris and his parents Lucy and Ray remain very much on guard, knowing every virus is life-threatening.

Chris suffers from the rare blood disorder HLH and still must undergo a raft of tests and medications, travelling back to Westmead Hospital weekly.

“If everyone was vaccinated, the chances of Chris picking up measles, mumps, chickenpox, etc, would be far, far less,” Ray said.

“In his condition, if he got a virus like whooping cough, his life would be threatened. His biggest enemy is a virus.”

On three occasions, it was viruses that triggered Chris’s HLH. For Lucy and Ray, helping Chris through his recovery is similar to having a vulnerable toddler again.

“Because he has a new bone marrow, his blood group has changed, and he now has to have all his baby injections again,” Ray said. 

But that cannot be done until his immune system recovers. 

“So, he cannot come into contact with people with an infectious disease, be it babies or adults.

“Yet, there are so many people out there now who believe immunisation is detrimental to their children’s health.”

Lucy fears younger parents did not experience the severe effects once common diseases like measles had in the past.

“They were not around to see the number of people getting those diseases and dying,” she said.

“The young ones coming through don’t know.”

Polio touched Ray close to home.

“In the ’50s, we lined up to have our polio shots. Our paper boy, who was six or seven years older than me, had polio and he died. It was not available when he was young. 

“The difference of those few years meant we survived and he didn’t.” 

Sticking to a severe regime of “X-Box therapy” with friends, Chris has spread the word.

“All my mates have had their flu shots,” he said. 

“I have had my mates over every week. If they are sick, they can’t be around me.”

He said the experience got him thinking about vaccination.

“I would definitely have my kids immunised and I would also want other people to get their kids done. I am not the only person that is immune-depressed.” 

His aim is a robust immune system and a ticket overseas.