Clinical trials show that a combination of pills, one still in the experimental phase and one that was just approved for the US market, are effective at curing hepatitis C, researchers say.

However, the cost of the treatment is expected to be at least $US80,000 ($A89,490) per year, making it out of reach to many of the 150 million people chronically infected with the liver disease worldwide, experts have said.

The New England Journal of Medicine published the latest data from a phase II clinical trial on daclatasvir and sofosbuvir.

Sofosbuvir, made by Gilead Sciences in California, was approved by the US Food and Drug Administration in December and has been given the brand name Sovaldi.

The trial included 211 people at 18 medical centres across the United States and Puerto Rico.

People enrolled in the study took a daily combination of 60 milligrams of daclatasvir – which has not been approved for market – and 400 milligrams of sofosbuvir, with or without a third drug called ribavirin that can cause anaemia.

A full 98 per cent of participants were considered cured, showing no detectable virus in their blood three months after the treatment ended.

Results were similar for people with the virus genotype 1, which is common in the United States, and those with genotypes 2 and 3 which are more common elsewhere.

The study was also the first to show that hepatitis C could be cured without the use of ribavirin.

Side effects of the combination included fatigue, headache and nausea.

Mark Sulkowski, medical director of the Johns Hopkins Center for Viral Hepatitis, said the research could soon transform treatments for hepatitis patients, who currently must get weekly injections of peginterferon.

“Standard treatments for the disease are going to improve dramatically within the next year, leading to unprecedented advances for the treatment of patients infected with the hepatitis C virus,” he said.

Concerns about the high cost of the 12-week drug treatment have been raised since Gilead’s pill was approved late last year.

The French organisation Doctors of the World has said the cost in high-income countries will be about $US11,000 per pill, resulting in a treatment cost of $US80-90,000.

“Sofosbuvir and other direct-acting antivirals coming out of late-stage development do not have to cost this much,” the group said in a statement after the FDA approval was announced.

“They can be produced generically for a tiny fraction of that price, just like HIV antiretrovirals.”

Some 350,000 people die of hepatitis C-related liver diseases annually, and as many as four million people are newly infected each year, according to the World Health Organisation.

Hepatitis C is caused by a contagious virus that can be transmitted through sharing needles, getting contaminated blood transfusions or having sex with an infected person.