Late last September, a conservationist group called Shark Allies got the press riled up about the possibility that “half a million” sharks could be killed to obtain squalene for use in Covid-19 vaccine adjuvants. NPR covered it, National Geo­graphic covered it, and so did many other press outlets. I put the number of sharks in quotes because I can’t find any basis for that particular claim.

In short: Americans shouldn’t need to be concerned about squalene in their Covid-19 vaccines until the end of this year, if ever.

In not-so-short: some vaccines — especially ones based on protein subunit technology — work better when administered along with a chemical adjuvant. There are a number of different types of adjuvants, and they work in different ways. Many times it’s not clear how adjuvants work, but their purpose is to improve the immune system response to the vaccine.

Some adjuvants include a chemical called squalene. Squalene is an oil that occurs in many plants and ani­mals, although not often in harvestable quantities. Some deep-sea sharks have huge livers with a lot of squalene, and that’s where most of the world’s squalene supply cur­rently comes from. And at least for now, all of the squalene used in pharmaceuticals comes from shark livers. Two popular squalene-based ad­ju­vants are MF59 from Novartis (used in the Fluad influenza shot in the US) and AS03 from GSK.

The Pfizer, Moderna, Janssen (Johnson & Johnson), and AstraZeneca vaccines don’t use adjuvants. The Novavax vaccine candidate that is just starting its Phase III trial in the US uses an adjuvant, but it’s a plant-derived non-squalene adjuvant called Matrix-M. Walter Reed’s vaccine candidate (not part of Operation Warp Speed) uses a non-squalene adjuvant combining bacteria-derived MPLA with plant-derived QS 21 (ALFQ).

Only one vaccine in the Operation Warp Speed portfolio is considering using a squalene adjuvant: a protein subunit vaccine from France’s Sanofi Pasteur. Sanofi is currently reformulating that vaccine after dis­ap­point­ing seroconversion results in their early-phase testing (not enough antibodies produced in older participants). Note: this is only for their protein subunit vaccine. Sanofi Pasteur is also working with Massachusetts-based Translate Bio to produce an mRNA vaccine, which is the same technology Pfizer and Moderna successfully used; that vaccine wouldn’t use an adjuvant. No working names have been given to those vaccines, making it a bit harder to keep them straight.

Elsewhere in the world, only two other vaccine candidates with squalene adjuvants are in clinical (human) trials:

• Clover’s SCB-2019 (Australia). Being trialed both with AS03 and with a non-squalene adjuvant, Dyna­vax’s CpG 1018.
• Medicago’s CoVLP (Canada). Being trialed with AS03.

One more vaccine candidate isn’t even in pre-clinical (animal) trials yet:

• Innovax’s XWG-03 (China). Will be trialed with “GSK pandemic adjuvant,” presumably AS03.

The press release from Shark Allies said that five Covid-19 vaccine candidates were using squalene ad­ju­vants, and I’ve only mentioned four. That’s because one candidate — Australia’s CSL Ltd. V451 with MF59 adjuvant — has been totally abandoned after early-phase volunteers began erroneously testing pos­itive for HIV.