“You don’t have to be a virologist or an epidemiologist or a physician to understand why this is a risk in the current day and age when” the novel coronavirus is still circulating,” said virologist Menno D. de Jong at the University of Amsterdam.

De Jong said people should be able to protest — but even demonstrators need to maintain social distancing.

“People need to be able to show their opposition to what has been happening in the United States and their solidarity with the affected individuals,” Paul Hunter, a professor at the University of East Anglia in the U.K., wrote in a statement. “But any mass gathering does pose a risk of increased transmission of COVID-19.”

Karl Lauterbach, a member of the German parliament for the center-left Social Democrats, tweeted a video of the demonstration in Berlin on Saturday and expressed concern that protesters weren’t keeping enough distance.