A landmark five-year trial has strengthened evidence that early use of antiretroviral drugs helps children combat the AIDS virus, doctors reported on Thursday.

Conducted in South Africa, the so-called CHER trial made history in 2007, after only two years, when it discovered that early treatment slashed the risk of disease and death from AIDS by 75 percent.

The astonishing finding prompted the World Health Organisation (WHO) to overhaul its treatment guidelines in 2010 for youngsters with the AIDS virus.

The WHO recommended that antiretroviral therapy be started immediately when HIV is diagnosed in children less than a year old, rather than wait until a threshold of virus infection is reached.

Now completed, the CHER trial takes early-use-is-good a step further, according to results reported in The Lancet.

Children who began an immediate course of drugs were able to interrupt their treatment, giving them a break from the powerful, potentially toxic drugs, researchers found.

Yet even with this interruption, the infants did far better than those who started treatment later.

On average, the children who received the deferred treatment began the drugs about 20 weeks after diagnosis.

Those who began an immediate course of 40 weeks of drugs were able to take a 33-week break before starting treatment afresh. And those who took an immediate 96-week course enjoyed a break of 70 weeks.

The trial was conducted at two sites in South Africa among 377 infants with HIV who were less than 12 weeks old.

The research marks the latest advance in knowledge about antiretroviral drugs, which revolutionised the fight against AIDS from 1996.

The drugs are a lifeline to millions, for they can roll back the virus to below detectable levels.

But if the drugs are stopped, the virus rebounds from boltholes, called reservoirs, in cells in the body.

Two other trials -- both small in scale and at a very early stage -- have recently raised hopes that hitting HIV with drugs very soon after infection can wipe out this hiding place.

An estimated 34 million people are infected with HIV worldwide, and about 1.8 million die each year.

Infants are especially vulnerable. If untreated, around half of infected newborns die before their second birthday.

The new work revives hopes that flourished in the late 1990s, before the reservoir problem was identified, that patients could get a temporary holiday from AIDS drugs.

"This important finding indicates we may be able to temporarily stop treatment and spare infants from some of the toxic effects of continuous ART [antiretroviral therapy] for a while, if we can monitor them carefully," said Mark Cotton, a professor at Stellenbosch University near Cape Town, who helped lead the study.

Caution, though, was sounded in a commentary by Robert Colebunders of the Institute of Tropical Medicine in Antwerp, Belgium, and Victor Musiime of Makerere University College of Health Sciences in Kampala, Uganda.

Treatment interruption is a risky option in poor countries which lack laboratory facilities to monitor levels of CD4 immune cells, they said.