“G” hasn’t just dominated the outbreak in Chicago — it has taken over the world. Now scientists are racing to figure out what it means.

At least four laboratory experiments suggest that the mutation makes the virus more infectious, although none of that work has been peer-reviewed. Another unpublished study led by scientists at Los Alamos National Laboratory asserts that patients with the G variant actually have more virus in their bodies, making them more likely to spread it to others.

The mutation doesn’t appear to make people sicker, but a growing number of scientists worry that it has made the virus more contagious.

“The epidemiological study and our data together really explain why the [G variant’s] spread in Europe and the U.S. was really fast,” said Hyeryun Choe, a virologist at Scripps Research and lead author of an unpublished study on the G variant’s enhanced infectiousness in laboratory cell cultures. “This is not just accidental.”