HIV patients whose immune systems remain intact can temporarily stop taking drugs without incurring health risks, say researchers in Geneva.
The team at the city's University Hospital believes the discovery could lead to major cost savings in the treatment of the disease, especially in Africa where millions have no access to drugs.
The Staccato study of 430 HIV patients in Switzerland, Thailand and Australia set out to discover whether "scheduled treatment interruptions" of antiretroviral therapy would have an adverse effect on their health.
Would their immune systems suffer and complications reappear, and would the virus become resistant?
To measure whether these fears were real or not, the Geneva team treated part of the study population continuously and the other part intermittently. The average interruption time was around four months, but ranged from four weeks up to two years.
Treatment was restarted when the CD4 cell count – which measures the strength of a person's immune system – fell below 350 cells per cubic millimetre of blood. Normal CD4 counts in adults range from 500-1,500, but this figure decreases as HIV progresses.
No ill effects
According to the findings, published in Saturday's edition of The Lancet medical journal, there were no Aids-related deaths and no Aids-defining illnesses observed.
"These results provide reassurance for patients who must or want to stop treatment, and they indicate that the risk of treatment resistance or complications is low, provided that your CD4 counts are high when you stop," Bernard Hirschel, head of the hospital's HIV/Aids unit, told swissinfo.
Hirschel says the main reasons for temporarily stopping drugs are cost, convenience and side effects. These can include nausea, vomiting, diarrhoea and lipodystrophy – the loss of body fat from the face, arms and legs.
He estimates that once extra CD4 monitoring – tests carried out every three months – is factored in, savings of 40 to 50 per cent can be made on treatment costs.
But the Staccato findings are likely to be challenged by the much larger SMART (Strategies for Management of Antiretroviral Therapy) clinical trial in the United States, whose results are due out within the next two months.
Hirschel says the SMART trial points to disadvantages in interrupting treatment. But he argues that the criteria used to stop and start treatment were not the same as in the Geneva study, and treatment interruptions were much longer on average.
Perhaps crucially, the baseline for resuming treatment in the US trial was set at a CD4 count of 250 – a factor that Hirschel says is being "hotly debated at the present time".
Far from being disheartened by the SMART trial, the Geneva team points to separate French and Italian studies of scheduled treatment interruptions, working with higher CD4 counts, that also produced positive results.
But Hirschel admitted it was clear from the conflicting findings that there was a need for further study.
swissinfo, Adam Beaumont in Geneva
It is estimated that antiretroviral therapy has reduced mortality rates among HIV patients in Switzerland by up to 90%.
The cost of the treatment in Switzerland is around SFr14,700 ($12,000) a year.
According to the Swiss Aids Federation, more than 20,000 men and women live with HIV/Aids in Switzerland.
Two people are diagnosed HIV-positive in Switzerland every day.
More than 40 million people worldwide are living with HIV/Aids, most of them in sub-Saharan Africa.
According to UNAids, the number of new HIV infections is believed to have stabilised. But the number of people living with HIV has continued to rise, due to population growth and the life-prolonging effects of antiretroviral therapy.
In sub-Saharan Africa, the number of people receiving treatment increased more than eight-fold from 100,000 to 810,000 between 2003 and 2005.
About one in six (17%) of the 4.7 million people in need of antiretroviral therapy in this region now receive it.