Prevention strategies need to target both early and chronic HIV infection

An analysis of transmission patterns in Lilongwe, Malawi shows that even if a highly effective HIV prevention intervention could reach 75% of people in chronic infection, it would never eliminate the HIV epidemic there. As a result, interventions that reduce transmission during early infection will also be required, Kimberly Powers told a late-breaker session at the Eighteenth International AIDS Conference in Vienna last Friday.

There are particular challenges to delivering prevention interventions to people in early infection. This is a relatively brief period of time during which people are typically unaware that they are infected. Current testing strategies and technologies are unable to identify all people who have early infection.

Early infection refers to first few months of infection. Time after this is called ‘chronic infection’.

During early infection, especially during the first few weeks, people are exceptionally infectious. Although it is known that a significant proportion of HIV transmission occurs during this time, previous modelling studies have given very different results as to the comparative contribution of early infection. Moreover the proportion is likely to vary from setting to setting, because of differences in sexual mixing patterns, the number of people with HIV and the number of people treated.

Kimberly Powers and colleagues wished to understand whether an HIV prevention strategy could ever be effective if it was only delivered to people in chronic infection.

They conducted a mathematical model, using data on HIV prevalence, viral load and sexual behaviour from Lilongwe, Malawi (a semi-urban setting, with a mature generalised epidemic). Heterosexual transmission is assumed to occur both within and outside steady partnerships. A person’s infectiousness was understood to vary over time, including within the period of early infection.

Using this data they estimated the proportion of HIV transmissions in Lilongwe that could be attributed to people in early infection, and found that it was 38% in 2010 (95% confidence interval 19 to 58%). Earlier on in the epidemic, this proportion was higher, but the figure is changing as more people live with chronic infection.

The researchers also wanted to predict the reductions in HIV prevalence which could be achieved by improved testing and prevention strategies during early infection.  They assumed that a prevention intervention was available which could almost eliminate onward transmission in those who received it.

They examined a number of scenarios in which the intervention reached different proportions of people in early infection and in chronic infection. They assumed that people in early infection would not receive any intervention at all during the first three weeks of infection. Moreover their analysis concentrated on scenarios where an intervention reaches up to 75% of a population, as it is probably unrealistic to expect higher levels of coverage.

They found that if only people in early infection got the intervention, then HIV prevalence could be reduced, but never eliminated. If 75% of people in early infection could be reached, prevalence might drop from around 14% now to 8% in 2030. Reductions would be smaller if fewer people were reached.

A slightly larger reduction could be achieved if 75% of people in chronic infection got the intervention, and no one in early infection got it.

However, if the intervention could reach 75% of people in chronic infection and 50% of people in early infection, prevalence would drop to about 1% by 2030. Similar results would be obtained if the intervention reached 75% of people in each group.

Powers concluded that early infection plays an important role in the HIV epidemic in Lilongwe, Malawi. “Our results suggest that it is time to determine the best ways to identify early index cases and the optimal prevention strategies to initiate during early HIV,” she said.

Powers K et al. The contribution of early HIV infection to HIV spread in Lilongwe, Malawi: implications for transmission prevention strategies. Eighteenth International AIDS Conference, Vienna, abstract FRLBC105, 2010.

View abstract and slides from this session on the official conference website.