Vaccines being made to protect people from swine flu are developed by killing sharks, shocking reports have indicated.
According to a report in National Geographic News, millions of doses of the pandemic H1N1/09 vaccine contain a substance called squalene, which is extracted from shark livers.
More commonly found in beauty products such as skin creams, squalene can be used to make an adjuvant, a compound that boosts the body's immune response.
The World Health Organization (WHO) recommends adjuvant-based vaccines, because they allow drug makers to create doses that use less of the active component, increasing available supplies.
Olive oil, wheat germ oil, and rice bran oil also naturally contain squalene, albeit in smaller amounts.
But for now, squalene is primarily harvested from sharks caught by commercial fishers, especially deepwater species.
"There are several very disturbing issues associated with use of shark-liver-oil squalene," said Mary O'Malley, co-founder of the volunteer-run advocacy group Shark Safe Network.
"The deepwater sharks targeted have extremely low reproductive rates, and many are threatened species," she added.
For example, one supplier has dubbed the gulper shark the Rolls-Royce of squalene-producing sharks, but the gulper is listed as vulnerable on the International Union for Conservation of Nature's (IUCN's) Red List of Threatened Species, meaning the species faces a high risk of extinction.
Although vaccines containing squalene have not yet been approved for use in the US', they are being distributed elsewhere, including Europe and Canada.
GlaxoSmithKline (GSK), a major swine-flu vaccine producer, announced in October this year that it had received orders for 440 million doses of vaccine containing adjuvant.
The adjuvant in GSK's vaccines, which have been administered in 26 countries so far, contains shark-liver squalene, company spokesperson Clare Eldred confirmed in a statement.
O'Malley, of the Shark Safe Network, estimated that GSK's 440 million doses would require at least 9,700 pounds (4,400 kilograms) of shark oil, based on the stated squalene content of 10.69 milligrams in a dose.
A shark-squalene alternative isn't yet an option for adjuvant vaccine makers, according to GSK's Eldred.
The drug company is currently looking at non-animal squalene sources, including olive oil.
But at the moment, "we are unable to find an alternative of high enough grade," she said.