Thursday January 14 2016
A drug called Truvada can help prevent HIV
"Giving healthy gay men HIV drugs 'could help reverse epidemic'," BBC News reports.
A modelling study looking at the effects of pre-exposure prophylaxis (PrEP), where drugs are used to prevent infection, estimated thousands of new cases of HIV could be prevented.
HIV infection continues to be a pressing concern for men who have sex with men. It is estimated there are around 44,500 men who have sex with men living with HIV in the UK. Without effective intervention strategies, that figure could rise to 57,500 by the end of the decade.
This mathematical model looked at a number of possible strategies, such as offering PrEP to men who have sex with men, regular testing, and providing early treatment for everyone who tests positive (known as "test and treat").
When the researchers looked at combinations of strategies at different levels of coverage, they found combining annual HIV testing with PrEP and test and treat could prevent 7,399 infections (43%), even if they only reached a quarter of men with a high risk of infection.
These figures are only estimates based on models created from other research findings. We don't know how well these strategies would work in the real world.
Truvada, a drug used in the US for HIV prevention in high-risk individuals, is moderately effective. A 2012 review estimated it reduced the risk of contractive HIV by around 49%. A conference presentation we discussed in 2015 increased that estimate to 86%.
Condoms remain the most effective way of preventing HIV, and have the added bonus of not causing side effects and providing protection against other sexually transmitted infections.
Where did the story come from?
The study was carried out by researchers from the London School of Hygiene and Tropical Medicine, the Medical Research Council Biostatistics Unit, the Centre for Infectious Disease Surveillance and Control, City University London, and University College London.
It was funded by Public Health England, the Medical Research Council, and the Bill and Melinda Gates Foundation.
The study was published in the peer-reviewed journal, The Lancet HIV. It is available on an open-access basis, which means you can read it for free online.
The study was widely covered by the UK media. Perhaps because of its complexity, reports highlighted a variety of figures for the potential number of infections prevented, from The Daily Telegraph's best-case scenario of 10,000, to the more realistic 7,399.
Not all of the reporting made it clear that the latter figure was an estimate of the effect of PrEP plus increased HIV testing and test and treat. The Daily Telegraph also overstated the reliability of the figures, failing to explain they are based on estimates from hypothetical models.
The Times claimed Truvada will soon be made available on prescription by the NHS. While this is a plausible prediction, it has not been officially confirmed.
What kind of research was this?
This mathematical modelling analysis used a model of how HIV spreads within populations to assess the possible effect of different interventions.
While this is useful information for public health chiefs considering different interventions, there is a wide margin of error.
What did the research involve?
The researchers used figures on HIV infections in men who have sex with men in the UK since 2001 to estimate transmission rates until 2020, if current HIV prevention strategies – encouraging safer sex and HIV testing – continue.
Then they used a mathematical model of how HIV spreads, using data from previous studies and surveys of sexual behaviour, to predict the effect of different interventions aimed at reducing the spread of the virus.
They did multiple calculations to assess the effects of the most successful interventions, in combination and assuming different levels of coverage.
The model included factors such as whether men were currently engaged in sexual activity and whether they had more than one new sexual partner in a year, which is considered to be high risk.
Data came from three surveys: one national survey from 2000 and two that included more recent data, but were London-based.
The interventions tested in the model were:
- HIV testing once a year
- HIV testing twice a year
- test and treat – where people receive treatment immediately if they test positive
- providing PreP to high-risk individuals
- reducing the number of repeated sexual partners men had
- reducing the number of one-off sexual partners men had
- decreasing the amount of unprotected sex men had with repeated sexual partners
The researchers looked at the effects of these interventions alone, assuming a "best-case" scenario where all men who have sex with men are reached, to see which were most promising. They then looked at the effects of more realistic coverage, at 25%, 50% and 75% of men reached.
The researchers took the most effective strategies from these results and looked at how they affected infection rates, both in combination and in different practical scenarios.
They also tested the model to look for the potential effects of so-called risk compensation, where men might take more risks if they are taking PrEP.
What were the basic results?
The best practical scenario was to combine once-yearly testing with test and treat and PrEP.
Assuming 25% of high-risk or infected men could be reached using each of these strategies, the researchers calculated this would prevent around 7,399 (interquartile range [IQR] 5587 to 9813) or 43.6% (IQR 32.9 to 57.9) of those infections expected if no additional prevention strategies were put in place.
Interquartile ranges are a statistical measure used to describe the upper and lower boundaries of an estimate, somewhat similar to a confidence interval.
Risk compensation reduces the effect of this strategy, but it would still prevent more infections than taking no additional action.
Looking at each intervention alone, with an assumed 100% coverage of men who have sex with men, PrEP had the biggest effect on new infections, followed by twice-yearly testing and a reduction in repeat sexual partners.
However, assuming 25% coverage, twice-yearly testing was most effective, followed by PrEP and test and treat.
How did the researchers interpret the results?
The researchers said that, "PrEP could prevent a large number of new HIV infections if other key strategies, including HIV testing and treatment, are simultaneously expanded and improved."
They warned that unless PrEP is introduced in the UK, the number of men who have sex with men being newly infected with HIV was unlikely to decrease before 2020.
This is a complex analysis of a number of different scenarios. It found giving PrEP treatment to HIV-negative men might have an important role to play in reducing the number of new HIV infections in the UK.
Like all mathematical models, the results rely on many different assumptions, some of which could turn out to be wrong. Although this study shows the potential for PrEP to make a big difference, we can't rely too heavily on its exact figures.
For example, one important limitation is the fact the study does not take into account the possible effects of drug resistance to HIV treatments, including PrEP.
If PrEP became less effective because of growing drug-resistant strains of the virus, it could have a big impact on how many infections can be prevented.
It's important not to focus entirely on PrEP, as the most effective of the practical scenarios assessed in the study also included regular HIV testing and prompt treatment.
For people at risk of HIV, regular testing combined with practicing safer sex is important. For those who already have the condition, treatment with antiretroviral drugs can keep you well for many years.
If you could be HIV positive, getting tested regularly means you can start treatment as soon as you need it, and increases your chances of keeping well.
PrEP as a preventative treatment for men who have sex with men is not available on the NHS at present, although NHS England is considering its use. This study may increase the likelihood that it will be made available to those at high risk of infection.
Condoms remain the most effective way to prevent HIV – and other STIs – in people who are sexually active.