Studies have shown that PrEP (pre-exposure prophylaxis) offers near complete protection against HIV if taken properly every day. Researchers are now testing it on young people in South Africa and the US.

Katherine Gill from the Desmond Tutu HIV Centre in South Africa said 148 adolescents (98 female, 50 male) in Cape Town and Soweto had enrolled in a study of the drug in the past year.

One in 10 people in South Africa have HIV and infections have dramatically increased among teenagers in the past decade. About 2000  females aged 15-24 are getting the virus every week -  a rate two-and-a-half times that of males the same age.

Sharifah Nalugo, a 21-year-old woman living with HIV in Uganda, said she was very excited about PrEP because of its potential to protect people against the virus, including those who are partnered to somebody with HIV.

"PrEP is going to be wonderful," the university student said. "People are going to embrace it because no one wants to be HIV positive."

Having been born to a mother with HIV, Ms Nalugo has felt a lot of anxiety about her status. When her mother told her she was HIV-positive at age nine, she was told to keep it a secret because of stigma in her community. Later, when her grandfather found out about her and her mother's HIV status, they were kicked out of his home.

As a teen, Ms Nalugo feared she would not get married or be able to have children because of HIV. But with the success of antiretroviral treatment, the emergence of PrEP, and strategies to prevent pregnant women from passing on the virus to their babies, she is optimistic about life.

"A lot of people love me ... I am lucky. I have had a lot of support," she said.

At the beginning of the study, the teens reported an average of one to two sex acts per week; 30 per cent had had two or more partners in the past year; 43 per cent reported infrequent condom use; and 38 per cent tested positive for sexually transmitted infections.

The participants were required to take PrEP pills daily for 12 weeks. They could opt out after that or choose to keep taking the medication. After three months, Dr Gill said none of the teens had HIV and 72 per cent of them reported that they had taken the pills as they had been told to.

Dr Gill said 85 per cent of the participants chose to keep taking the medication beyond three months.

"For the first time we have something to offer adolescents aside from condoms," she said at the  AIDS 2016 Conference in Durban.

Another study of PrEP in 78 gay and bisexual adolescent males in the US found that the medication was well tolerated and produced few side effects. Three participants acquired HIV during the study but it was unclear if the drug did not work or they did not adhere to instructions to take the pills daily.

Dr Sybil Hosek of the Stroger Hospital of Cook County Health and Hospitals System said the study was now being submitted to the US Food and Drug Administration to see if PrEP could be approved for people under 18. While some participants still got HIV, she said the number would have been higher in the group if they had not been taking the drug.

President-elect of the International AIDS society Linda-Gail Bekker said she hoped 2016 would be the dawn of a global "PrEP era", however she said the drug strategy was too expensive for most people.

"Despite the strong science supporting PrEP, its implementation in the real world has been quite limited," she said.

"Just this week we saw a UNAIDS report showing that we're only 2 per cent of the way towards reaching the UNAIDS goal of having three million people on PrEP by 2030, so there really is a great deal of work to be done."

Many factors are contributing to young people acquiring HIV in Africa, including limited sex education in schools; low condom use; sexual assault; poverty driving teens into sex work; and stigma which discourages testing.

There is also a large cohort of teens and people in their 20s who were born with the virus in the 1990s and 2000s, before perinatal infections were being routinely prevented through antiretroviral treatment.

While some of these young people are taking antiretroviral drugs that control the virus, making them virtually non-infectious, health workers say many struggle to adhere to the arduous medication regime because of the chaotic nature of their lives.

Julia Medew attended the AIDS 2016 conference courtesy of the Doherty Institute.