An advanced HIV vaccine trial in Africa has been halted after data showed the injections offered only limited protection against the virus, researchers said on Tuesday.
The vaccine, made by Johnson & Johnson, is part of a long line that offers little defense against HIV, one of medicine’s most intractable adversaries. A vaccine candidate even increased the risk of infection.
Another trial was halted last year in South Africa after another experimental vaccine failed to provide sufficient protection. Some 1.5 million people were infected with HIV worldwide in 2020, and 38 million are living with the infection.
Scientists were appalled by the most recent failure.
“I should be used to it by now, but you’re never used to it – you always put your heart and soul into it,” said Glenda Gray, the trial’s principal investigator and chair of the South African Medical Research Council. Dr Gray has been working on the development of an HIV vaccine for over 15 years.
Entirely new approaches may be needed. This month, Moderna announced that it would test a vaccine based on the mRNA platform used to design the company’s coronavirus vaccine.
The trial, called Imbokodo, tested an experimental vaccine on 2,600 young women deemed to be at high risk of HIV infection in five countries in sub-Saharan Africa. Women and girls accounted for almost two-thirds of new HIV infections in the region last year.
The trial was funded by Johnson & Johnson, the Bill and Melinda Gates Foundation, and the National Institutes of Health.
The vaccine relied on an adenovirus called Ad26, modified to transport fragments of four HIV subtypes around the body in the hope of eliciting an immune response that could defend itself against infection.
Mitchell Warren, executive director of AVAC, an advocacy group that advocates for the prevention and treatment of AIDS, said canceling the trial was a “reality check” amid the enthusiasm for new vaccine technologies.
“It’s a great reminder that HIV is a pathogen unlike any other in its complexity,” he said. “We know the platform worked, but what do we put in it? Because this virus infects the exact same immune system that we are trying to strengthen with a vaccine. “
Participants in the Imbokodo trial, which began in 2017, received two initial injections and two boosters over the course of a year. The researchers followed the number of new infections in the placebo and vaccine groups from month 7 (one month after the third vaccination) to month 24.
Over two years, 63 of the 1,109 participants who received the placebo were infected with HIV, compared to 51 of the 1,079 participants who received the vaccine, giving the vaccine an efficacy rate of 25%.
Previous studies, including one in Thailand, had indicated that the type of antibody this vaccine elicited may be sufficient to provide good protection against HIV for at least an initial period.
“But in South Africa, the higher HIV incidence rates mean you need something much more potent,” Dr Gray said. “The type of immune responses induced was simply not enough to stop the high attack rates we are seeing in Africa.”
When disappointing data showed a low rate of efficacy, guidelines set before the trial dictated that it should be stopped. A vaccine that offered only 25% protection risked giving women a “false sense of security,” said Dr Gray.
But a parallel trial that uses a different iteration of this vaccine will continue, Johnson & Johnson said. It is being tested on men who have sex with men and transgender people in eight countries including Poland, Brazil and the United States.
This study, called Mosaico, tests the vaccine against different HIV subtypes in different populations and may produce different efficacy results.
Dr Gray said the lesson from the failed trial is to understand why it worked for the 25% of people protected and not for the rest, and then try to translate those clues into a recipe for a future vaccine. .