The group says the importance of increasing vaccine protection in developing countries has been shown with the emergence of the Omicron variant, adding "concerted global co-operation" could reduce the risk of COVID mutations.

Headed by health coalition End COVID For All the letter also calls on the government to launch a $50 million campaign to combat vaccine hesitancy.

Spokesman Rev Tim Costello said COVID would continue to mutate and spread until low-income countries caught up with the rest of the world's vaccination rates.

Just three per cent of people in low-income countries are fully vaccinated, he said.

"This is unfair, immoral, dangerous for those communities and dangerous for Australia," Mr Costello said.

"COVID-19 really isn't over for anyone until it's over for everyone.

"While Australia enjoys some of the highest vaccination rates in the world, it won't mean much if COVID mutates into a vaccine-resistant strain.

"New and unknown variants threaten to undo progress even in nations with high vaccine coverage."

The letter referenced the government's "important contributions" helping Indo-Pacific neighbours to access vaccines, and its initial investment in COVAX, but added "this crisis is far from over".

It also notes "grave concerns" regarding global vaccine inequity.

Regarding a further call for $100 million to the Coalition for Epidemic Preparedness Innovations, Mr Costello said the pandemic had a "catastrophic impact" in the fight against other diseases.

He said the number of people treated for drug-resistant tuberculosis dropped by 19 per cent in 2020, while people helped by HIV prevention services dropped by 11 per cent.

"Devastatingly, it is predicted that 150 million more people will end up in extreme poverty as a result of the pandemic," he said.

"Inaction risks decades of development and humanitarian efforts. We cannot in good conscience sit idly by and let it happen when we have the financial firepower and resources to prevent it."

Australian Associated Press