On August 31, 2021, Johnson & Johnson announced that a mid-sized clinical trial of their HIV vaccine failed to protect participants against HIV. The trial was conducted in South Africa among 2,600 women at high risk of infection. At the end of the roughly four-year study, there were no significant differences in HIV acquisition between those who received the vaccine and those who got placebo.
It is the latest disappointment in a line of vaccine candidates that stretches back to the 1990s. The challenge of creating an HIV vaccine is cast in particularly harsh relief when compared to the speed with which scientists developed a COVID vaccine.
The backbone of this latest HIV vaccine is based on the same technology as the highly effective J&J COVID vaccine. Why, then, did it fail for HIV? This will be the subject of detailed analyses in the coming months, perhaps years, but we know some things about HIV that have always made a vaccine extraordinarily difficult.
Some had hoped that the rapid success in making COVID vaccines would translate into new hope for an HIV vaccine.First, unlike COVID, there are no scientifically documented cases of HIV clearance by the immune system, and thus no signposts pointing to the kinds of immune responses we need a vaccine to induce. Second, the immense genetic diversity of HIV and its array of tricks to evade immunity dwarf those of SARS-CoV-2, the virus that causes COVID-19.
Some had hoped that the rapid success in making COVID vaccines would translate into new hope for an HIV vaccine. In fact, though, it was the converse. It was the long history of vaccine development intended for HIV that allowed J&J to develop a COVID vaccine so rapidly.
Likewise, the technology behind the Moderna and Pfizer COVID vaccines was first conceived as a potential vaccine for HIV. Although Moderna recently announced that it plans to start a trial of its technology as an HIV vaccine, history teaches us that when it comes to HIV, nothing is quite so simple.
We may rightly feel very fortunate to have not just one but several highly effective COVID vaccines. But fortune, as 19th century chemist and microbiologist Louis Pasteur commented, favors the prepared mind. Decades of novel ideas and hard work developing concepts for HIV vaccines ensured that the most advanced technologies were ready for testing in COVID. Can we come full circle and parlay our success against SARS-CoV-2 into an effective HIV vaccine? It’s hard to be optimistic but each successive failure only makes the challenge more compelling.
Dr. Johnston is vice president and director of research.