Sharks produce squalene, a natural oil made in their livers, which is an ingredient in several COVID-19 vaccine candidates.
Half a million sharks could be killed for their natural oil to produce coronavirus vaccines, according to conservationists.
Squalene is currently used as an adjuvant in medicine - an ingredient that increases the effectiveness of a vaccine by creating a stronger immune response.
British pharmaceutical company GlaxoSmithKline currently uses shark squalene in flu vaccines.
The company said it would manufacture a billion doses of this adjuvant for potential use in coronavirus vaccines in May.
Around 3,000 sharks are needed to extract one tonne of squalene. Shark Allies, a California-based group, suggests that if the world's population received one dose of a COVID-19 vaccine containing the liver oil, around 250,000 sharks would need to be slaughtered, depending on the amount of squalene used.