* GSK to start large trials testing protective injection
* Under-skin implants seen as promising long-term option
* New HIV cases still running at 1.9 million annually
By Ben Hirschler
LONDON, Nov 29 (Reuters) - Scientists are taking the battleto prevent HIV to the next level with large-scale trials set tostart using injections to protect vulnerable groups such as gaymen and women in Africa for at least two months.
Further down the road, the hope is to producematchstick-sized implants containing slow-release drugs -similar to existing under-the-skin contraceptive devices - thatcould offer year-long protection.
Companies with drugs involved include GlaxoSmithKline, Gilead Sciences and Merck.
The initiatives build on the success of Gilead's once-dailypill Truvada, which has proved remarkably effective at stoppingHIV infection during sex.
Clinical studies show such pre-exposure prophylaxis, orPrEP, can cut the risk of catching the virus by more than 90percent, as long as people take their pills regularly. Theproblem is many do not.
Some women in trials in Africa, for example, said they werereluctant to have HIV tablets in the house for fear of whatpartners or neighbours would think.
An injection given in a clinic, experts argue, would addprivacy and ensure steady drug levels. An implant in the armmight even combine contraception and HIV protection in one go.
"The more options there are the better and I think for someindividuals injections will be great," said Jean-Michel Molina,professor of infectious diseases at Hospital Saint-Louis inParis.
"Now that we know antiretrovirals have great potential toprevent HIV infections, it is time to really assess other waysto deliver these drugs."
The need remains acute. Despite treatment advances that haveslashed AIDS deaths, around 1.9 million people still catch HIVeach year - a number that hasn't budged since 2010. Newinfections among gay men are actually increasing.
The United Nations AIDS programme warned last week that theproblem now threatened progress in ending the global epidemic,while the World Health Organization has recommended PrEP for allgroups at substantial risk of HIV infection.
STILL NO VACCINE
GlaxoSmithKline's majority-owned ViiV Healthcare unit,working with U.S. government agencies and the Bill & MelindaGates Foundation, hopes to add the first injectable PrEP.
It plans to start a four-year trial as soon as next monthtesting its experimental drug cabotegravir in gay men in theAmericas and Thailand, with a second trial next year assessingthe medicine in African women.
Two separate studies evaluating cabotegravir in combinationwith another drug for HIV treatment were launched this month.
"The holy grail is a vaccine, but we don't have a vaccineyet," said Myron Cohen of the University of North Carolina atChapel Hill, who is involved in the ViiV prevention studyprogramme and believes new options can help rein in HIV.
He is also working on another prevention trial giving peopleantibodies via an intravenous drip.
Gilead, meanwhile, is running a late-stage study assessingits next-generation HIV drug Descovy as an alternative oralPrEP, since it has milder side effects than Truvada.
In the long run, Cohen and other HIV experts are especiallyexcited by slow-release drug implants. Implants have yet toprove themselves in human trials, although an experiment inbeagles last year with a Gilead drug produced promising results. Products from GSK and Merck are also seen as implant options.
The size of the HIV prevention market remains uncertain andprice will be an issue, especially in Africa, but some industryanalysts believe it could be substantial.
Truvada, the only medicine so far approved for HIVprevention, is now being used for PrEP by 80,000-90,000 peoplein the United States, accounting for 35-45 percent of the drug'srevenue in the third quarter.
It is starting to gain traction, too, in Europe, with Franceoffering free supplies, while in Britain and other markets,where it is not paid for by the government, people are turningto online "buyers clubs" to get cut-price generics.
There is resistance, however. A French government campaignthis month promoting HIV awareness, including PrEP, was attackedby several French mayors.
Some have also criticised PrEP for diluting the "safe sex"message of condom use, especially as it will not prevent othersexually transmitted infections (STIs).
But Sheena McCormack of University College London arguesthis misses the point. "Sometimes people can't see the wood forthe trees. The STI that lasts a lifetime and costs governments alot of money is HIV."
(Editing by Alexandra Hudson)
Glaxosmithkline (GSK)