Melbourne researchers have turned one of the world's most-used drugs into a nasal spray which they hope could prevent COVID-19 transmission.

Northern Health medical divisional director Don Campbell said he had a "crazy idea" that the blood-thinning drug heparin could stop the virus growing in cells.

But it wasn't until his wife asked "well, what are you going to do about it?" that he got to work.

Nearly two years later, with the help of researchers at Melbourne, Monash and Oxford Universities, his team has been able to replicate international findings that heparin can block the transmission of COVID-19 and prevent infection.

The spray coats the nose but does not go down into the lungs. The researchers say it is cheap, easy to distribute and is expected to be effective against mutant strains of the virus including the Omicron variant.

"It won't matter if a new variant comes along, this drug will block that protein from infecting the cells," Professor Campbell said.

"I'm very confident that we can demonstrate that it will work, and people will be using this before they go to the shops and before they go to school."