Fact Check-Differing colour shades of blood do not indicate whether someone has had a COVID-19 vaccine 

Different shades of blood do not indicate whether someone has received a COVID-19 vaccine, despite people reporting otherwise online.

Social media users have shared a photo of two full blood bags – one a crimson red; the other maroon – alongside a claim that they show blood taken from a vaccinated and unvaccinated individual respectively.

The photo has since been used as alleged proof that blood from people vaccinated against COVID-19 is unsafe, with one person writing on Facebook: “What would you do if you need blood transfusion and the only ‘choice’ is the infected one on the right?” (here). 

Further examples of the image on social media are viewable here , here , here , here and here.

However, two medical experts told Reuters this claim is false. While it is true that blood can come in different colours and shades, it has nothing to do with COVID-19 vaccines.

“The image is demonstrably false,” said Skyler Johnson, an assistant professor at the Department of Radiation Oncology at Huntsman Cancer Institute, University of Utah School of Medicine, who was speaking to Reuters via email.

“There is no theoretical or biological plausibility to the idea that vaccines could change the color of someone’s blood.”

Also speaking to Reuters, Dr Paul Strengers, a consultant at the International Plasma and Fractionation Association, said blood can come in “a variety of colours”, but agreed there are none that are vaccine related.

He said: “Blood comes in a variety of colours, including red, blue, green and purple. This rainbow of colours can be traced to the protein molecules that carry oxygen in the blood.

“Different proteins produce different colours. For example, if someone has eaten a very fatty meal, the colour of blood on the next day will show that, after cooling, the surface of the (yellow) blood plasma has turned into white. The reason is that at the surface the fat in blood is floating on the plasma and a layer of white fat is present.”

Vaccination, however, enhances the concentration of specific antibodies in the body “as a consequence of the trigger (antigen) in the vaccine,” said Strengers, who added: “[Specific] antibodies have no colour.”

Explaining a more likely possibility for the different shades of red blood, Johnson told Reuters: “The image, although it’s difficult to be sure, likely represents a venous blood draw (darker) and an arterial blood draw, and could even be from the same patient.”

Moreover, blood also changes shade if stored for a period of time, where it undergoes a metabolic change to a non-oxidative state (here).

Reuters previously addressed the claim that it is unsafe to receive blood from a vaccinated individual. (here).


False. Differing shades of red blood do not indicate whether someone has a health issue following a vaccination, nor does it indicate whether someone has received a COVID-19 vaccine.

This article was produced by the Reuters Fact Check team. Read more about our fact-checking work  here.