Vaccine from Thailand Shows Promise in South Africa

Glenda Gray, executive director of the Wits Health Consortium’s perinatal HIV research unit in South Africa, presented data today at the HIV R4P conference in Cape Town indicating that the prime-boost vaccine candidates initially tested in the RV144 trial in Thailand—the only HIV vaccine trial to date to show any efficacy—induced cross-clade immune responses in a Phase I safety trial conducted in South Africa, with immunogenicity similar to or greater than that of the responses induced in Thai volunteers. The vaccine, designed for testing in Thailand where clade B and recombinant E/A HIV predominates, was found 31% effective in preventing HIV infection among Thai volunteers. Meanwhile, clade C HIV is the predominant strain in South Africa.

This January, researchers here will start a Phase I study evaluating a clade C-specific HIV vaccine regimen, along with a new adjuvant, known as MF59, aimed at boosting the potency of the vaccine candidates and the durability of the immune responses it induces. Gray said on Tuesday that if results from this Phase I study are encouraging, then Phase III efficacy trials of this vaccine regimen are expected to begin sometime in 2016 or 2017. Efficacy trials will involve as many as 7,000 volunteers.

Even if the vaccine regimen is only partially efficacious, Gray doesn’t see this as a problem. “A partially efficacious intervention to prevent HIV acquisition would have public health benefit,” she says. Ultimately regulators will decide, but licensure for a vaccine could come with efficacy as low as forty or fifty percent. Researchers are already considering how different partially effective prevention strategies might be used in concert. “When we found that male circumcision worked, we rolled that out in our trials,” she says.

Combining a partially effective vaccine with antiretroviral-based pre-exposure prophylaxis could be another approach, Gray says.

The MF59 adjuvant, developed by the pharmaceutical company Novartis, is currently used to boost responses to flu vaccine. Novartis, however, earlier this year sold most of its vaccine unit to rival GlaxoSmithKline in a US$7 billion deal. It’s unclear how Novartis’s sale may impact the production of the vaccine candidates for the South African trial. But for now Gray says there aren’t any delays. “It hasn’t had any effect. Not yet.” – Michael Dumiak