MIAMI — Science's steady march to find a vaccine capable of ending the coronavirus pandemic may come at the expense of another species: sharks.
Miami shark researchers say they're concerned about a key ingredient used to make vaccines more effective, squalene — an oily substance found in plants and even human skin — but is particularly concentrated in shark livers.
The practice of using shark-derived squalene as a booster to stimulate a stronger immune response to a vaccine is not unique to the coronavirus vaccine. The compound has been shown to be safe and effective in millions of doses of vaccines, primarily in Europe, said Liza Merly, a shark immunologist at the University of Miami's Rosenstiel School of Marine and Atmospheric Science.
"We don't exactly know what it is about this oil that allows that to work the way it does," Merly said.
But squalene in vaccines has been shown to create more robust immune responses, and there are a handful of COVID-19 vaccine candidates that use it for that purpose, most of them partnered with GlaxoSmithKline, which manufactures a squalene-derived component for vaccines.
If one of the vaccine candidates using that component proves to be effective, it could create a global demand for squalene that might threaten wild shark populations, according to Shark Allies, a nonprofit dedicated to protecting wild sharks.
The nonprofit produced a crude estimate: It would take about 500,000 sharks to produce squalene for the billions of vaccine doses needed to inoculate everyone on the planet twice. That spurred international headlines and prompted push back from GSK, which has argued that the estimate is far too high. But the company has declined to identify the source of its squalene, other than to say that it's harvested from sharks that were fished for other purposes, and that is what worries shark experts.
Catherine Macdonald, a marine conservation biologist and ecologist at UM's Rosenstiel School, calculated a more advanced estimate and arrived at a slightly lower projection of 360,000 sharks needed to produce enough squalene to power the billions of vaccine doses.
But Macdonald said the number matters less than the lack of transparency in the shark-fishing industry, which is under-regulated. Shark fishing has been known to harm wild populations, Macdonald said, primarily in search of fins, but also while hunting for squalene, which is commonly used in cosmetics.
A sudden spike in squalene demand would be a significant concern, she said, in part because the liver oil is more abundant in deep sea sharks that are vulnerable to overfishing.