Fact Check

Do COVID-19 Vaccines Change the Color of Human Blood?

Some organisms do have blue blood — just not humans.

Published Oct. 12, 2021

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COVID-19 vaccines change the color of human blood.

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In late 2021, some users took to social media to claim that COVID-19 vaccines changed the color of human blood. A number of iterations of the allegation were present on social media and, as fact-checkers at USA Today, The Associated Press, and AFP previously reported, it appears to have originated in a Sept. 17 Instagram post:


“Left vs. Right= non vax vs. VAX,” read the post, which also featured two bags of what appeared to be differently red-hued bags of blood that looked “like a bag of blood clots.”

Some users used the photo to argue that the American Red Cross didn’t “want blood from inoculated people” because “it looks disgusting!!!”

This is false. In an email to Snopes, the American Red Cross said that the claim was “simply untrue.”

“There is no substance to the claim that COVID-19 vaccine changes the color of blood. At the American Red Cross, we visually inspect all donated units and have not seen that COVID-19 vaccinated blood units change the color of blood,” wrote spokesperson Kate Wilkes,

Blood in human veins is always red, never blue, though it can sometimes look blue through our skin — an optical illusion that occurs because blue light does not penetrate as far into tissue as red light. If a blood vessel is deep enough, the eyes see more blue than red light reflected because of how the blood absorbs red wavelengths. (Blue blood does exist in the natural world — for instance, in horseshoe crabs.)

But the hue of blood can vary naturally because of the way blood interacts with oxygen. A protein called hemoglobin, which contains a red-colored compound heme, is responsible for carrying oxygen through the blood stream. As The Conversation, a nonprofit news organization, reported previously, heme contains an iron atom that binds to oxygen and transports from the lungs and throughout the body. When oxygen is bound to its iron, blood can turn a bright, candy apple red. Without oxygen, it appears as a darker red color.

Minor variations in individual levels of bilirubin, an orange-yellow pigment related to red blood cells, oxygen, iron, lipids and red blood cell count, among other factors, can contribute to changes in blood color, added Wilkes.

But there is no known instance where a COVID-19 vaccine changed the hue or color of blood.

Difference in hue between arterial (brighter) and venous (darker) blood. Public Domain

“A donor’s immune response is not impacted by giving blood. Donating blood after receiving a COVID-19 vaccine does not reduce a donor’s protection from the virus. Similar to other vaccines such as measles, mumps or influenza, the COVID-19 vaccine is designed to generate an immune response to help protect an individual from illness,” said Wilkes.

That is backed up by a June 2021 study published in the peer-reviewed journal Transfusion, which determined that current donor screening guidelines are acceptable in light of the pandemic. These guidelines do not require testing samples for SARS-CoV-2 virus but do require that donors be screened for symptoms of COVID-19 and other infections.

“This finding is good news for thousands of patients who may need a blood transfusion because of surgery or a disease that causes anemia, such as a rare blood-related condition or leukemia,” said Dr. Simone Glynn, study author and chief of the Blood Epidemiology and Clinical Therapeutics Branch at the National Heart, Lung, and Blood Institute, in a news release.

At the time of this writing, the Red Cross said that there is an emergency need for blood and platelets and the Red Cross warns that such misinformation could potentially deter people from donating lifesaving blood to help hospitals and patients in need.

“Individuals who have received a COVID-19 vaccine are still eligible to donate blood and platelets. Knowing the name of the manufacturer of the vaccine they receive is important in determining blood donation eligibility. The Red Cross only collects blood from individuals who are healthy and feeling well at the time of donation,” wrote the organization in a Sept. 27 statement.


Bakkour, Sonia, et al. “Minipool Testing for SARS-CoV-2 RNA in United States Blood Donors.” Transfusion, vol. 61, no. 8, 2021, pp. 2384–91. Wiley Online Library, https://doi.org/10.1111/trf.16511.

Bilirubin Test - Mayo Clinic. https://www.mayoclinic.org/tests-procedures/bilirubin/about/pac-20393041. Accessed 12 Oct. 2021.

“Blood In Your Veins Is Always Red, Not Blue.” Snopes.Com, https://www.snopes.com/news/2019/08/28/blood-in-your-veins-is-always-red-not-blue/. Accessed 12 Oct. 2021.

“Covid-19 Vaccines Do Not Affect Blood Color.” Fact Check, 22 Sept. 2021, https://factcheck.afp.com/http%253A%252F%252Fdoc.afp.com%252F9NA6BT-1.

“COVID-19 Vaccines Do Not Change Color of Blood.” AP NEWS, 20 Sept. 2021, https://apnews.com/article/fact-checking-170435327923.

Emergency Blood Shortage — Donor Turnout Reaches Lowest Levels of the Year amid Delta Variant Outbreak. https://www.redcross.org/about-us/news-and-events/press-release/2021/emergency-blood-shortage-donor-turnout-reaches-lowest-levels.html. Accessed 12 Oct. 2021.

https://www.redcross.org/about-us/news-and-events/press-release/2021/emergency-blood-shortage-donor-turnout-reaches-lowest-levels.html. Accessed 12 Oct. 2021.

“Fact Check: COVID-19 Vaccination Has No Effect on Blood Color.” USAToday, https://www.usatoday.com/story/news/factcheck/2021/09/26/fact-check-covid-19-vaccines-dont-change-blood-color/5821288001/. Accessed 12 Oct. 2021.

Fact Check: There IS NOT A Visible Difference Between The Blood Of Vaccinated And Unvaccinated People | Lead Stories. https://leadstories.com/hoax-alert/2021/10/fact-check-there-is-not-a-visible-difference-between-the-blood-of-vaccinate-and-unvaccinated-people.html. Accessed 12 Oct. 2021.

“Is Horseshoe Crab Blood Required for COVID-19 Vaccines?” Snopes.Com, https://www.snopes.com/fact-check/horseshoe-crab-blood-covid-vaccine/. Accessed 12 Oct. 2021.

“U.S. Blood Donations Are Safe under Current COVID-19 Screening Guidelines.” National Institutes of Health (NIH), 1 June 2021, https://www.nih.gov/news-events/news-releases/us-blood-donations-are-safe-under-current-covid-19-screening-guidelines.

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Madison Dapcevich is a freelance contributor for Snopes.

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