Injections that slowly and continuously release HIV medication into the blood are being tested.

Early trial data from 309 patients showed jabs every one or even two months worked as well as daily pills - which is how antiretroviral medication is currently taken.

The results are being presented at the IAS Conference on HIV Science.

Daily antiretroviral medication holds the virus back, prevents HIV destroying the immune system and stops the development of Aids.

The success of therapy has led to deaths related to Aids halving since 2005 to around one million a year.

Aids deaths halve as more get drugs

But the medication is a burden - someone diagnosed aged 20 could end up taking more than 20,000 HIV tablets in a lifetime - and some people struggle, leading to HIV coming back and the virus resisting the effects of treatment.

The trial was conducted at 50 centres in the US, Canada, Germany, France and Spain.

When people were diagnosed with HIV they were initially given oral therapy to bring the virus under control.

Then they spent 96 weeks getting either traditional daily pills, monthly injections or injections every two months.

The results, published in the Lancet medical journal, showed that by the end of the study:

• 84% of patients on daily doses were still suppressing the virus

• 87% with injections every four weeks

• and 94% with injections every eight weeks.

Side effects - including diarrhoea and headache - were similar in all groups.

However, this is still a relatively small trial and a larger and longer-term one is already underway to try to confirm the results.

The work was funded by the companies making the drugs: ViiV Healthcare, which is mostly owned by GSK, and Janssen, which is part of Johnson & Johnson.

Dr David Margolis, one of the researchers from ViiV Healthcare, said: "Adherence to medication remains an important challenge in HIV treatment.

"The introduction of single tablet medication represented a leap forward in antiretroviral therapy.

"Long-acting antiretroviral injections may represent the next revolution in HIV therapy by providing an option that circumvents the burden of daily dosing."

'Milestone'

The drugs companies are packaging two of their medicines (cabotegravir and rilpivirine) into tiny nanoparticles, which can be injected into muscle.

This gives long-lasting protection as the nanoparticles break down and release their medicinal contents into the body.

There are 36.7 million people living with HIV around the world and only 53% have access to the current medication.

In a review of the research, professors Mark Boyd and David Cooper from the universities of Adelaide and New South Wales, commented: "[The] study marks yet another remarkable milestone in the evolution of HIV therapeutics."

However, they warned some people may find it easier to have daily pills than having to see a doctor for an injection every one or two months.

"There will inevitably be a trade-off between the convenience of not having to adhere to oral therapy and the inconvenience and discomfort associated with injectable long-acting antiretroviral therapy.

"It is possible that injectable antiretroviral therapy will be more attractive the less one must be injected."