We now know
that starting antiretroviral therapy early, pre-exposure prophylaxis (PrEP) and
vaginal microbicides can all have an impact on HIV transmission, Victor de
Gruttola told a satellite session at the International AIDS Society conference (IAS 2011)
in Rome on
Sunday. But researchers now need to do more than establish efficacy, he said.
need to identify the mechanisms by which interventions do and do not work in
different communities. They need to get to understand the characteristics of
sexual networks, sexual behaviour and local epidemiology that influence their
effectiveness. And they need to compare the impact of providing a stand-alone
intervention with that of combined packages of interventions.
at the satellite, which had been organised by AVAC and the European AIDS Treatment Group,
emphasised the importance of implementation research – identifying barriers to
the implementation of prevention interventions and developing strategies to
de Gruttola from the Harvard School of Public Health and Timothy Hallett from
Imperial College London suggested there is no single best intervention – or even
best package of interventions, but that this will depend on the characteristics
of different communities and epidemics.
different settings, researchers need to identify the combination of prevention
interventions which could keep the spread of HIV under control. They also need
to establish the breadth of programme coverage that is required.
presented some results from a basic mathematical model which aimed to identify
the impact and cost of providing antiretroviral therapy to 80% of people at a
number of different CD4 counts, PrEP to varying proportions of young people,
PrEP to most people of all ages, or a combination thereof.
For each level of
spending, Hallett identified the programme that would have the greatest impact
– at the lowest levels of spending identified, this would be antiretroviral
therapy alone. Should there be budget available to fund more than making
therapy available for all with diagnosed HIV, policy makers should then provide
PrEP for young people, and then for people of all ages.
model’s results change if baseline assumptions shift. If the costs of PrEP are
actually lower than Hallett estimated (because drug prices come down), or if it
turns out to be more expensive to get people diagnosed early and on to treatment
(because testing promotion has less impact than anticipated or because new
health services need to be provided), strategies with a greater reliance on
PrEP would start to make more sense.
modelling studies need to consider other issues. Interventions – and
combinations of interventions – will have different levels of effectiveness in
different places, depending on a vast range of local factors which researchers
are only beginning to get to grips with.
example, Victor de Gruttola mentioned assortativity: the tendency for people
who have many sexual partners to choose partners with the same characteristic.
When this is the case, interventions will have less impact than when there is
important local factors are the number of transmissions that are due to people who
are themselves recently infected, the proportion of people with HIV who are
diagnosed and linked to care and the proportion of HIV-negative people who can
be provided with an intervention.
noted that, although we know from the HPTN 052 trial that early initiation of
treatment can reduce transmission to stable partners by 96%, this does not mean
that changing treatment guidelines will bring about a 96% reduction in new
many people are diagnosed late for this to be possible. While early treatment
strategies rely on early diagnosis, Sheena McCormack of the UK's Medical Research
Council said that frequent HIV screening is not always an acceptable
modelling work suggests that, even to achieve a 60% reduction in new infections
through early treatment, testing would have to be so frequent that 60% are
diagnosed within a year of infection, 90% of diagnosed people would have to be
treated, 87% would need to be virally suppressed within six months of starting therapy, with only a 1% drop-out rate from treatment programmes.
modifications in these highly optimistic assumptions can wipe out the predicted
impact. On the other hand, a combination of interventions would be more
resilient in real-life conditions.
there not be the resources to make treatment available for everyone who needs
it, its impact could be increased by prioritising its provision to people at
higher risk of passing their infection on.
McCormack argued that the next prevention trials need to show that it is feasible
to deliver interventions in a service setting, rather than with a great number
of extra resources or with excessive demands placed on participants. Requirements
for clinic visits, HIV tests and laboratory monitoring should be cut back,
while users should be advised that PrEP may only be used around the time of
sex, rather than on a daily basis. These measures will reduce the cost of
interventions and increase their acceptability to users, she said.
out that a key question for a pilot PrEP study in the UK is whether a
significant number of gay men are actually interested in taking it.
acceptable interventions are more likely to be used consistently, and Sheena
McCormack said that adherence is key to all the interventions discussed: “It’s
all about behaviour,” she said. This applies as much to condom users as it does
to people using a microbicide, PrEP or antiretroviral treatment.
This news report is also available in French.