We came across this image being circulated via multiple posts on Facebook, along with captions in varying languages:

The post appears to be a screenshot of a messaging app, and comes with a photo of two bags of blood – one in a much deeper shade of red than the other. Along with the photo is a message saying that the bag on the left, which was allegedly taken from an unvaccinated individual “looks reddish and alive”. The other bag, which was purportedly taken from a vaccinated individual, “looks downright scary and purplish black”.

The message then ends saying that one should therefore ensure that they’re getting a blood transfusion from an unvaccinated individual.

Different shades of red?

A fact-check by AP News quoted Dr. Stephanie Halene, chief of hematology at the Yale Cancer Center, who said that she was “not surprised at the different colours of the bags in the photo [as] the colour of blood can vary depending on the level of oxygen in it”.

Skyler Johnson, an assistant professor at the Department of Radiation Oncology at Huntsman Cancer Institute, University of Utah School of Medicine, told Reuters that “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.”

In a fact-check by AFP, we read that Dr PJ Utz, professor of immunology and rheumatology who runs a Stanford University research lab, also reiterated the point that “the colour is dictated by how much oxygen is in the blood”.

Dan Milner, chief medical officer at the American Society for Clinical Pathology, added “blood is always drawn from veins, which carry deoxygenated blood back towards the heart, and put in blood bags that are hermetically sealed”, and “this is why blood in donation bags is quite dark, particularly when compared to the bright red oxygenated blood visible after a cut.”

A fact-check by US Today consulted Dr. Pampee Young, chief medical officer of biomedical services at the American Red Cross, and she stated that “At the American Red Cross, we visually inspect all donated units and have not seen that COVID-19 vaccinated blood units change the colour of blood.”

The experts consulted in the fact-checks all rubbished the claim that the difference in blood colour is due to vaccines.

Therefore, the claim that vaccination causes a change in blood colour is false.

As for potential concerns regarding blood donation post-vaccination, we referred to the Singapore Health Sciences Authority’s website and read that the blood bank has implemented a new blood donation eligibility guideline for donors who have received a COVID-19 vaccine.

As seen, the minimum deferral period is one week, for individuals who took the mRNA (Pfizer, Moderna) or inactivated virus (Sinovac) vaccines with no side effects. Individuals who experience the usual side effects from the vaccines are advised to wait either 1 or 4 weeks after the side effects are resolved.

HSA also explained that the 4-week waiting period for live-attenuated (Astra Zeneca, J&J) vaccine is due to patient safety consideration, because blood from a recently vaccinated donor may contain an infective agent which although not harmful to the donor, may theoretically pose a risk to patients who are immune-suppressed or immunocompromised such as cancer patients.

Therefore, while there is indeed advice that individuals should wait a short period post-vaccination to donate blood in light of the potential temporary side effects from the vaccines, there is no evidence or indication that the blood of vaccinated individuals are not suitable for donations as insinuated in the social media posts.