Model suggests HIV vaccine still has key role in ending AIDS

Even a modestly effective HIV vaccine would likely be cost-effective and could make a major contribution to a sustainable response to the global HIV/AIDS epidemic, especially in combination with the scale-up of other interventions including prompt initiation of antiretroviral therapy (ART) and pre-exposure prophylaxis (PrEP), according to a report in the January 5 edition of PLoS ONE.

Prevention approaches including condoms, antiretroviral treatment as prevention (TasP) and PrEP have already brought about substantial reductions in new HIV infections, but there are still too many people becoming infected worldwide to bring the epidemic to a halt.

Thomas Harmon of the International AIDS Vaccine Initiative (IAVI) and colleagues performed a modelling study to estimate the impact of an HIV vaccine, combined with interventions included in the UNAIDS Investment Framework Enhanced (IFE), in low- and middle-income countries.

The IFE, proposed in 2013, explored how maximising existing interventions and adding emerging prevention options could reduce new HIV infections and AIDS-related deaths in low- and middle-income countries, the authors noted as background. This report describes additional modelling that looked more closely at the potential health impact and cost-effectiveness of HIV vaccines.

The researchers devised an epidemiological model to explore the potential impact of HIV vaccination in low- and middle-income countries in combination with other interventions through 2070. Sensitivity analyses looked at variations in vaccine efficacy, duration of protection, coverage and cost.

The model looked at three possible scenarios:

• Current trends – assumes that incremental linear scale-up of ART and prevention of mother-to-child transmission from 2010 to 2013 continues, off-setting the natural increase in new infections due to population growth and resulting in a steady annual incidence; eligibility for ART remains at < 350 cells/mm³ and ART coverage is capped at 80%. (Current WHO guidelines call for treatment for everyone with HIV regardless of CD4 count, but this has not yet been implemented in many countries.)
• 50% scale-up of IFE – assumes that UNAIDS IFE targets are only achieved halfway, based on linear scale-up from 2013 coverage to 50% of IFE target levels in 2020.
• Full scale-up of IFE – assumes that the IFE targets are fully achieved, based on linear scale-up from 2013 to the target levels in 2020.

In the current trends scenario, incremental scale-up of existing interventions results in a flat trajectory of new infections in low- and middle-income countries, with around 1.6 million annually in 2070. 50% scale-up of IFE would reduce the number of new annual HIV infections to approximately 1 million in 2070, and if UNAIDS IFE goals were fully achieved, new annual HIV infections would decline to 550,000 in 2070.

Adding a three-dose HIV vaccine with 70% efficacy, five years of protection and high coverage, introduced in 2027 along with the full scale-up scenario, would reduce annual infections by 44% over the first decade, by 65% over the first 25 years and by 78% (to around 122,000) in 2070. Under the same scenario a vaccine with 30% efficacy would reduce new infections by 44% (to around 306,000) while a vaccine with 90% efficacy would produce an 87% reduction (to around 74,000) by 2070.

Adding the same 70% effective vaccine to the current trends scenario would reduce new infections by 85% (to around 260,000) and adding it to the 50% scale-up scenario would reduce incidence by 82% (to around 184,000) by 2070. That is, the impact of the vaccine would be greater if the IFE targets were not fully achieved, according to the authors.

Adding PrEP, TasP and an HIV vaccine – individually or in combination – to the full IFE scale-up scenario would reduce the number of annual new HIV infections in 2070 by 29%, 34%, 78% and 91%, respectively, with vaccination providing the strongest single benefit despite being introduced later. A combination of PrEP, TasP and a vaccine could reduce the number of annual infections to around 49,000 in 2070.

The researchers also presented evidence showing than an HIV vaccine would be cost-effective under a wide range of scenarios.

"Even a modestly effective vaccine could contribute strongly to a sustainable response to HIV/AIDS and be cost-effective, even with optimistic assumptions about other interventions," the study authors concluded. "Higher efficacy would provide even greater impact and cost-effectiveness, and would support broader access."

"First generation AIDS vaccines may not achieve the very high efficacy levels of most other currently licensed vaccines, and structural, cultural and social barriers may make it challenging to meet assumed coverage rates for some target populations," they caution, "but the model shows that vaccines of relatively lower efficacy and uptake still have the potential to substantially reduce new HIV infections."

"The data suggest that under certain circumstances vaccination could prevent more new infections with HIV than other new prevention options," they wrote. "However, the modelling also confirms that no single option can solve the problem alone. A variety of prevention and treatment options can complement each other in ensuring that the specific needs of specific populations in different circumstances are met in order to maximize the reduction of new HIV infections."

"These new analyses underscore the powerful potential of an AIDS vaccine to help save and improve the lives of millions in a cost-effective manner," IAVI president and CEO Mark Feinberg stated in a press release. "It is clear that we must continue to expedite development of an effective HIV vaccine alongside the critical efforts to accelerate and sustain broad and equitable access to effective antiretroviral therapy and new approaches for pre-exposure prophylaxis."