Paired with a biannual testing programme, a combination drug used to prevent HIV infection has the potential to improve average per-person survival by nearly one year and block more than 270,000 HIV transmissions in India over a period of 15 years, says a study.

The once-a-day pill, called pre-exposure prophylaxis (PrEP), can reduce the risk of HIV acquisition by over 85 per cent when taken consistently.

The new study, published in the journal Clinical Infectious Diseases, suggests that making PrEP available to men who have sex with men (MSM) and people who inject drugs (PWID) in India may be a cost-effective way of curbing the epidemic in the country.

"We know PrEP helps stop the spread of infection; the question is whether it is a good use of limited resources? Our study shows that PrEP is a cost-effective strategy for both MSM and PWID in India. For these groups, especially in areas with high HIV incidence, PrEP is worth rolling out," says lead and corresponding author Pooyan Kazemian of the Massachusetts General Hospital (MGH) in the US.

Using a widely-published mathematical model to project clinical and economic outcomes of HIV disease, the authors compared various prevention and testing programmes - including annual or biannual HIV testing alone, as well as PrEP paired with HIV testing - that could help reduce HIV infection and therefore improve survival for these high-risk groups.

Their findings suggest that PrEP would increase survival substantially by reducing infection risk, while more frequent HIV testing would provide little additional benefit.

"While the World Health Organization recommends quarterly HIV testing for those on PrEP, our analysis identifies PrEP with semi-annual testing as the cost-effective HIV prevention strategy for MSM and PWID in India," said co-author Nagalingeswaran Kumarasamy of the Voluntary Health Services in Chennai.

However, the authors noted that a nationwide PrEP rollout would be quite costly.

If nearly 60 per cent of MSM and PWID across India participated in the programme, it would increase HIV care expenditures by over $900 million over a five-year period, the study said.

"Our findings suggest that geographic areas of highest HIV incidence should be targeted first to reduce the budget required," said co-author Nomita Chandhiok of the Indian Council of Medical Research in New Delhi.