Most flu shots do not contain mercury

Flu season is officially underway in the United States. As of Nov. 2, respiratory viruses, including the flu and respiratory syncytial virus (RSV), are currently surging across the country, especially in children and infants. 

Since the onset of flu season, the VERIFY team has been receiving a lot of questions about the flu shot, such as whether it’s safe to get the flu vaccine and COVID-19 booster at the same time — it is. 

VERIFY viewer Paula wants to know if this year’s flu shot contains a particular ingredient. 

“Do flu shots contain mercury?” Paula asked our team in a text message.  

THE QUESTION

Do flu shots contain mercury?

THE SOURCES

• Food and Drug Administration (FDA)
• Centers for Disease Control and Prevention (CDC)
• Clare Rock, M.D., associate professor of medicine in the Division of Infectious Diseases at Johns Hopkins School of Medicine, and associate professor of epidemiology at Johns Hopkins Bloomberg School of Public Health
• CVS Pharmacy

THE ANSWER

Most flu shots do not contain thimerosal, a mercury-based preservative. It's only found in some shots that are packaged in multi-dose vials. There is also no evidence of harm caused by thimerosal. 

WHAT WE FOUND

A small percentage of flu shots do contain thimerosal. Thimerosal is a mercury-based preservative that has been widely used since the 1930s to prevent contamination in multi-dose vials of medicines and vaccines, including the flu shot. 

Thimerosal contains ethylmercury, which is a different form of mercury than methylmercury — the kind that causes mercury poisoning. The Centers for Disease Control and Prevention (CDC) says ethylmercury is safe to use in vaccines because it’s processed differently in the body, meaning it is less likely to build up in a person’s system —and because it’s used in tiny amounts.

Thimerosal is used only in multi-dose vials. The majority of vaccines are manufactured in single-dose containers. This means most flu vaccines administered in the U.S. do not have any thimerosal in them, according to the Food and Drug Administration (FDA) and CDC.

More from VERIFY: Yes, Pfizer is planning to increase the cost of its COVID-19 vaccine by as much as 400%

“In general, there is no mercury in most of the flu vaccine that we see,” Clare Rock, M.D., an associate professor of medicine at Johns Hopkins School of Medicine, said. “There is a mercury-derivative that's in tiny, tiny, minute portions in multi-dose vials to act as a preservative and basically prevent against any bacteria or germs growing inside the vial.” 

This flu season, 93% of flu shots “will be thimerosal-free or thimerosal-reduced” a CDC spokesperson told VERIFY in an email. A table on the CDC website also shows that three out of the nine flu shots available during the 2022-2023 flu season contain thimerosal.

Data from many studies show no evidence of harm caused by low doses of thimerosal in vaccines. The use of the preservative has significantly declined in the U.S. since 1999 after the FDA requested (but didn’t require) all licensed vaccine manufacturers remove thimerosal from vaccines as a precautionary measure. 

Thimerosal has not been used in vaccines for children since 2001. Some states, such as California, New York, and Washington, have laws on the books that prohibit administering mercury-containing vaccines to pregnant women or to children younger than three years of age.

More from VERIFY: VERIFY Fact Sheet: RSV illness

VERIFY contacted several healthcare providers and pharmacies to ask whether they offer flu vaccines that do not contain thimerosal to their patients. 

In an email, a CVS spokesperson said, “we offer several FDA-approved and CDC-recommended flu vaccines with different formulations to meet patient needs, none of which contain thimerosal.” 

On its website, CityMD, one of the largest urgent care providers in New York and New Jersey, says it offers a “preservative free, with no mercury” flu vaccine to its patients. Cornell Health, which partners with Wegmans Pharmacy to provide annual flu vaccination clinics at Cornell University, also offers thimerosal-free flu shots. Enloe Medical Center in Chico, California, is also administering “preservative free” flu vaccines this year, according to its website. 

While most flu shots do not contain thimerosal, if you want to make sure you receive a thimerosal-free flu shot, you can request one through your healthcare provider or pharmacist. 

More from VERIFY: Yes, you can get the omicron COVID-19 booster and the flu shot at the same time