Vaccine for Aids elusive

WORLD Aids Vaccine Day was observed earlier this week to educate communities around the world about the importance of HIV vaccine research.

Despite the undeniable success of antiretroviral therapy (ART) in improving the lives and life expectancy of people living with HIV, the virus continues to wreak havoc in our population.

While new infections have gone down from a peak of 16 000 infections per day in 1997 to just over 4 500 per day, worryingly an additional 1.7 million people became newly infected with HIV in 2018, increasing the total number of people living with the virus worldwide to 38 million. This is an untenable situation.

Global efforts have ensured that 25 million people receive ART. Unfortunately, ART does not eradicate HIV.

The virus rebounds soon after treatment is interrupted, regardless of how long a person has taken it. This is because HIV persists in cells and tissues, even during treatment, in what is called the viral reservoir.

Moreover, the reality is that all antiretroviral drugs have potential toxicity, and access to treatment for everyone remains challenging and comes with a huge economic burden.

In addition, infection with HIV is still a cause of stigmatisation and, in many cases, discrimination. Many cure strategies have been attempted and, while some are promising, they have considerable toxicity and much more refinement will be needed before they can be implemented in clinical practice. Ensuring universal access to cure strategies will also be challenging.

In the absence of a cure, the most effective way to eradicate an infection is through preventive vaccination.

The eradication of smallpox is a case in point. Unfortunately, despite considerable optimism in the early stages of the HIV pandemic, a vaccine has remained elusive.

The main reasons are the genetic diversity of the virus – it mutates as it divides, making it difficult for the immune system to find a target to attack – and the difficulty in figuring out what kind of immune response is needed for protection.

Since the discovery of HIV in 1983, there have been a number of vaccine trials that made use of different strategies, all of which have failed. The only glimmer of hope came from the Thai trail, RV144, which reduced the risk of infection by 31%.

Recently, a similar study was undertaken in South Africa to confirm the results of this trial, called the HVTN702 study. However, in February, the data-safety monitoring board recommended that the study be stopped due to lack of efficacy.

This failed trial demonstrated the concerning state of the HIV epidemic in South Africa once again. The trial found an HIV incidence of 4% among women, meaning that four out of every 100 women are becoming infected with HIV every year.

This is despite the fact that the trial offered participants the best HIV prevention methods currently available, including pre-exposure prophylaxis, against a background of high levels of ART use in the population.

The dynamics of transmission are still poorly understood, and the epidemic is clearly out of control. In the aftermath of this trial, some have started questioning whether we will ever have an effective vaccine. But the HIV field, including patients and scientists, is nothing if not robust.