The development of a successful vaccine to combat the spead of COVID-19 could result in the deaths of as many as a half-million sharks worldwide, according to a conservation group.

The U.S.-based nonprofit shark-conservation organization Shark Allies has collected almost 88,000 signatures on a petition demanding that pharmaceutical companies stop using sharks as a source of an organic compound called squalene, an oil-like substance that is produced in all plants and animals.

Squalene is especially useful as a vaccine additive called an adjuvant, which is used to stimulate a strong immunilogic reponse from the body in fighting disease. Shark Allies, using October 2 World Health Organization (WHO) figures in an undated article, says there are 193 candidate vaccines worldwide in clinical (42) or preclinical (151) evaluations, with 19 of the 193 using adjuvants and five of those employing shark-based squalene.

(Updated [October 15] WHO numbers show 198 candidate vaccines, with 42 in clinical trials and 156 in preclinical evaluations.)

Shark Allies says that if a COVID-19 vaccine using shark-based squalene is proven effective, and if two doses per person are required, as many as a half-million sharks could be killed just for the compound stored in their livers. The group notes that upwards of three million sharks are already killed annually for squalene alone.

(A 2013 paper in the science journal Marine Policy set the number of sharks killed annually by humans worldwide at about 100 million, or almost 11,000 per hour, and noted that the actual number could be as high as 273 million. About half that number is killed for their fins, used in shark-fin soup, a luxury food item mainly consumed in China and Vietnam. Scientific American estimated in 2013 that the shark trade overall is worth about $630 million annually.)

"It is likely that more than one dose of a COVID-19 vaccine will be needed per person, or that a COVID-19 vaccine would need to be given seasonally, similar to flu vaccines," Shark Allies notes. "If shark squalene continues to be used, this could mean significant losses for shark populations..."

The nonprofit group also says on its petition page that there ae alternatives to shark-based squalene for vaxccine adjuvants and other uses: "Squalene made from shark liver oil is used most commonly because it is cheap to obtain and easy to come by, not because it is more effective than other sources...Squalene for adjuvants can be produced from yeast, bacteria, sugarcane, olive oil, and possibly even algae. For example, Amyris, one of the producers of squalene based in California, uses a process that derives squalene from sugarcane. In their most recent statement, they explained that they can produce enough squalene for 1 billion vaccines in one month or less."

More than 50 species of sharks are hunted for their livers, according to Shark Allies, and some of them—such as the whale shark, the basking shark, and the great white shark, three of the world's largest species of shark and, therefore, with proportionately larger livers containing more squalene—are threatened or endangered, according to the International Union for Conservation of Nature.

Squalene is also used in the cosmetics industry as a moisturizer and antioxidant, in some sunscreens, and as a health supplement.