Just in time for Halloween, researchers from the historically Transylvanian city of Romania, called Cluj-Napoca, announced the first-ever artificial blood that could be used without fearing life-threatening side effects of prior models.

The new artificial blood relies not on hemoglobin, like typical artificial bloods, but hemerythrin — a protein extracted from sea worms that is then mixed with water and salts. Doctors can use the artificial blood to reduce infection rates during blood donation, and to supply lost stores in patients for several hours or even up to a day, researcher Dr. Radu Silaghi-Dumitrescu says.

“Mice treated with this ‘Made in Cluj’ artificial blood did not experience any side effects, and this is precisely what we want,” he told Romanian news outlet Descopera, adding that human trials can only take place once the team is 100 percent sure mice experience no toxicity from the blood. “Tests on humans are an extra gentle subject – authorization…represents a huge risk.”

Hemerythrin mirrors hemoglobin in its duties — transporting oxygen throughout an organism’s body — but differs in which organisms those duties are performed. Nearly all vertebrates use hemoglobin to ferry oxygen within red blood cells, while hemerythrin is found only in certain invertebrates, namely worms and valves. The hemerythrin-based artificial blood isn’t the deep red normally associated with blood, but more of a translucent yellow, although Silaghi-Dumitrescu said they were able to color it red for familiarity.

Hemerythrin is preferable to hemoglobin, the researcher added, because hemerythrin does not easily succumb to the physical and chemical stress when introduced into a living organism. Hemoglobin tends to lose its integrity through such exposure.

The research team was confident the artificial blood could find its way to clinical trials on humans within the next year or two, when they can assess whether their creation can be safely transfused into people. Silaghi-Dumitrescu also claims the breakthrough could lead to “instant blood” that would come in portable containers and turn into artificial blood just with the addition of water. He and his research team have been building their artificial blood for the past six years.

Hemoglobin-based oxygen carriers (HBOCs) are not approved by the U.S. Food and Drug Administration (FDA) because of their potential toxicity. Despite performing the same function as hemoglobin itself, HBOCs work outside red blood cells.

“This cell free Hb can cause high blood pressure; Hb can also escape the blood vessels and damage the kidneys and other organs,” the FDA said in a statement. “Therefore, FDA has not approved any HBOCs for use in the United States, and the regulatory agencies of most other countries also have not approved HBOCs.”