Experts say the ingredients in the COVID-19 vaccine developed by Pfizer and German partner BioNTech, which was authorized Friday by the U.S. Food and Drug Administration, looks pretty standard for a vaccine.
In a letter to the FDA, Pfizer listed the ingredients in its vaccine. They can be organized into four basic categories:
Active ingredient
- 30 mcg of a nucleosidemodified messenger RNA (modRNA) encoding the viral spike (S) glycoprotein of SARS-CoV-2.
Fats
- lipids (0.43 mg (4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis(2-hexyldecanoate), 0.05 mg 2[(polyethylene glycol)-2000]-N,N-ditetradecylacetamide, 0.09 mg 1,2-distearoyl-sn-glycero-3- phosphocholine, and 0.2 mg cholesterol)
Salts
- 0.01 mg potassium chloride
- 0.01 mg monobasic potassium phosphate
- 0.36 mg sodium chloride
- 0.07 mg dibasic sodium phosphate dihydrate
Sugar
- 6 mg sucrose
“Nothing too surprising there,” said Dr. Matthew Heinz, a hospitalist based in Tucson, Arizona. “It’s a normal way of packaging up medications for people.”
The only active ingredient in the vaccine is the messenger RNA encoding the viral spike of SARS-CoV-2. That describes the modified mRNA that contains the code for cells to make the spike protein specific to the virus that will help create antibodies to attack it.
The next key ingredient on the list is the lipid molecule, a small ball of fat, that contains four components. Some of the components, like cholesterol, are natural to the body. Other components, like the polyethylene glycol (PEG), are not.
PEG is used in a range of pharmaceutical, cosmetic and food products, according to FullFact.org, a registered charity and nonprofit company from England that fact-checks and debunks false or misleading claims.
There have been rare cases of allergic reactions to products with high concentrations of PEG, such as some commonly used laxatives, but the Pfizer vaccine contains a tiny amount of the substance – only enough to maintain the integrity of the lipid molecule.
Heinz said that if there was any part of the vaccine that could trigger a mild allergic reaction, it could be one of the fat components, but that is very rare.
“We’re talking about a number of relatively mild reactions that you can count on one hand” out of tens of thousands of people in the study, he said.
The lipid molecule protects the mRNA. Without it, the mRNA would be broken down inside the body before delivering the genetic code to the cell. This protective ball of fat is very fragile, which is why the vaccines have to be stored at subzero temperatures with dry ice or a special freezer until five days before use.
The list of salts may seem like complicated chemicals, but Heinz said they are variants of salt natural to the body that keep the pH – the acidity or basicity of a solution – balanced. The combination of these salts helps the body absorb the solution and protects the fatty molecule and mRNA.
“That’s just pretty basic chemistry,” Heinz said.
The sugar protects the vaccine during freezing. Sucrose is a glucose molecule that tastes sweet and stabilizes the vaccine in subzerotemperatures.
Before the vaccine is injected into a patient’s arm, health care providers add an extra 2.16 mg of sodium chloride per dose. The additional salt is meant to further balance the pH right before injection.
“It’s a lot of science. These vaccines take a lot of work,” Heinz said. But “people should not be in any way concerned or bothered by that list (of ingredients).”
