Certain COVID-19 vaccine candidates could increase susceptibility to HIV, warns a group of researchers who in 2007 learned that an experimental HIV vaccine had raised in some people the risk for infection with the AIDS virus. These concerns have percolated in the background of the race for a vaccine to stem the coronavirus pandemic, but now the researchers have gone public with a “cautionary tale,” in part because trials of those candidates may soon begin in locales that have pronounced HIV epidemics, such as South Africa.
Some approved and experimental vaccines have as a backbone a variety of adenoviruses, which can cause the common cold but are often harmless. The ill-fated HIV vaccine trial used an engineered strain known as adenovirus 5 (Ad5) to shuttle into the body the gene for the surface protein of the AIDS virus. In four candidate COVID-19 vaccines now in clinical trials in several countries, including the United States, Ad5 similarly serves as the “vector” to carry in the surface protein gene of SARS-CoV-2, the viral cause of the pandemic; two of these have advanced to large-scale, phase III efficacy studies in Russia and Pakistan.
In today’s issue of The Lancet, four veteran researchers raise a warning flag about those COVID-19 vaccine candidates by recounting their experience running a placebo-controlled AIDS vaccine trial dubbed STEP. An interim analysis of STEP found that uncircumcised men who had been naturally infected with Ad5 before receiving the vaccine became especially vulnerable to the AIDS virus. The vaccine, made by Merck, had been the leading hope for what was then a 20-year search for a shot that could thwart HIV. But after the STEP results appeared, the field went into a tailspin. “It took a decade to recover,” says one of the co-authors of the Lancet correspondence, Lawrence Corey of the Fred Hutchinson Cancer Research Center.