New Analysis Reveals Low HIV Transmission Risk at Suppressed Viral Loads
A new analysis published in The Lancet suggests that people living with HIV who maintain low, detectable levels of the virus and adhere to their antiretroviral therapy (ART) have an extremely low risk of transmitting it to their sexual partners. The study found that the risk of sexual transmission of HIV is almost zero at viral loads of less than 1000 copies per milliliter of blood, commonly referred to as having a suppressed viral load.
ART involves taking daily medication to treat HIV, which reduces the amount of the virus in the body, preserves immune function, and lowers the morbidity and mortality associated with the virus. Without ART, individuals living with HIV can have viral loads ranging from 30,000 to over 500,000 copies per milliliter, depending on the stage of infection. Previous research has shown that people with viral loads below 200 copies per milliliter have zero risk of sexually transmitting the virus. However, there was less clarity regarding the risk of transmission at viral loads between 200 and 1000 copies per milliliter.
To fill this knowledge gap, researchers from the Global Health Impact Group and the World Health Organization conducted a systematic review of research studies published between January 2000 and November 2022. They identified eight studies involving 7762 serodiscordant couples across 25 countries. Serodiscordant couples are those in which one partner is living with HIV.
Of the 323 sexual transmissions of HIV detected in the studies, only two involved a partner with a viral load of less than 1000 copies per milliliter. In both cases, the viral load test was performed at least 50 days before transmission, suggesting that the individuals’ viral load may have increased afterward. Furthermore, when the studies provided data on the full range of viral loads in partners with HIV, at least 80% of transmissions involved viral loads greater than 10,000 copies per milliliter.
According to Dr. Lara Vojnov from the World Health Organization, the ultimate goal of ART for people living with HIV is to maintain undetectable viral loads. This not only improves their own health but also prevents transmission to their partners and children. She added that these new findings are significant as they indicate that the risk of sexual transmission of HIV at low viral loads is almost zero. This provides an opportunity to destigmatize HIV, promote the benefits of adhering to ART, and support individuals living with HIV.
While lab-based plasma sample tests offer the most sensitive results for viral load testing, they are not feasible in many parts of the world. Therefore, the study’s findings support the use of simpler testing approaches, such as dried blood spot samples, for categorizing viral loads in clinical decision-making.
Dr. Laura Broyles, the lead author of the study from the Global Health Impact Group, emphasized that it is extremely rare for individuals with low levels of HIV to transmit the virus to their sexual partners. She noted that the conclusion should encourage the expansion of alternative viral load testing methods that are more accessible in resource-limited settings. Improving access to routine viral load testing could help people with HIV lead healthier lives and reduce transmission of the virus.
The study’s authors acknowledge some limitations in their research, such as imprecise data due to variations across the studies in the definitions of low viral load, as well as differences in viral load testing timing and patient follow-up. Given the extremely low number of transmissions, large sample sizes would be needed to develop more precise estimates. Additionally, the findings do not apply to HIV transmission from mother to child, which has distinct factors that influence the risk and prevention of transmission.
Presented at the 12th International AIDS Society Conference on HIV Science (IAS 2023), the study’s findings have also prompted the World Health Organization to publish an updated policy brief on sexual transmission prevention and viral load testing guidance. The aim is to further prevent HIV transmission and support global efforts to achieve undetectable viral loads. It is believed that these new insights into the minimal risk of HIV transmission at low viral loads will help shape public health strategies and contribute to the fight against HIV/AIDS.
