But none of them banked on having to contend with widespread social upheaval caused by the death of George Floyd, which has brought tens of thousands of people into the streets and into close contact in cities across the country to protest police violence.

The demonstrations are a new challenge to health officials’ still-early efforts to test and trace new infections, a key step to swatting down new clusters of cases. And scientists aren’t of one mind on the question of how well the virus could spread in protests, which are taking place in open air, with many—but not all—participants wearing masks.

The demonstrations are also happening as restrictions lift around the country and people tire of preventive measures, which will make it harder to unpack whether new cases are caused by the demonstrations, or by behavior that would have occurred in the course of a calmer reopening.

“Protests and large gatherings make it difficult to maintain our recommended social-distancing guidelines and may put others at risk,’’ said Kristen Nordlund, a spokeswoman for the U.S. Centers for Disease Control and Prevention. “It’s too early to know what, if any, effect these events will have on the federal COVID-19 response.”

Though it may take weeks for new cases to begin to show up in the data, and while a definitive answer on transmissions will be difficult to establish, top officials leading the U.S. response to the pandemic have expressed concern about the situation. Many of the protesters are black and other people of color, groups that have been harder-hit by the virus than white populations. 

“I do worry,” said Deborah Birx, a medical officer on the White House Coronavirus Task Force. “I worry terribly about the peaceful protests,” she said this week. “We are really trying to work with each of the mayors to expand testing availability over the next week or two so that the individuals who are involved in the peaceful protests can get tested and really know their status before they unknowingly spread it to the elderly.”

Crowded conditions, chanting and shouting, and prolonged exposure to others create an environment where coronavirus could more easily spread, said William Schaffner, an infectious disease professor at Vanderbilt University in Nashville, Tennessee. The demonstrations may be an accelerant, he said.

“This is complicated because the whole country is opening up,” Schaffner said. “Whether we can sort out increases due to these demonstrations from the general increase which we are already experiencing in many parts of the country, I’m not sure.”

‘Wait and see’ 

The topic is fraught, with some officials struggling to address the health risks without dismissing the protests. The CDC declined to have an official discuss it, as did the Mayo Clinic, one of the premier U.S. academic medical institutions. Anthony Fauci, the head of the U.S. National Institute of Allergy and Infectious Diseases and one of the leaders of the U.S.’s response, side-stepped the subject during an online interview this week when he was asked about the protests and efforts to re-open states.

“We’ve seen pictures and photos and TV clips of people very much congregated, no masks, together on a boardwalk, on a beach, in a pool,” Fauci said during the interview with Howard Bauchner, editor-in-chief of the Journal of the American Medical Association. “That has been and continues to be a concern to me. We’re not going to know what the effect of that is for at least a couple more weeks. It likely is three weeks or more. We need to wait and see.”

Before the protests, most so-called super-spreading events that have been tied to major outbreaks in the U.S. occurred among relatively small groups of people interacting inside.

A single infected person who attended choir practice on March 10 in Mount Vernon, Washington, just north of the location of the first cases in the U.S., infected 52 of the 61 people present. An employee at Biogen Inc. infected dozens of people while attending a company meeting in Boston in February, with those who picked up the pathogen spreading it to more than half a dozen other states.

How the virus spreads among people outdoors, however, is much less well understood. There was a super-spreader event at an Italian soccer match earlier this year. But elsewhere, large gatherings that have stirred fears of wider outbreaks haven’t produced them. Protests in the U.S. at many statehouses against the lockdowns haven’t—so far—produced large jumps in infection rates.

For now, many officials are trying first to halt the violence in the streets. While officials in place like Chicago and Minnesota have encouraged protesters to observe social distancing and even quarantine, most municipalities aren’t visibly trying to trace contacts, push people to physically separate, or institute any other additional public-health surveillance.

Masks and testing

One thing infectious disease doctors are sure of is that protesters should keep wearing masks.

“I would advise to anyone who is going to these demonstrations, and people really have it in their hearts to participate, then wear a mask by all means, try to keep yourself as separate as possible from others and rather than yelling and chanting, how about holding up a sign?,” said Schaffner.

In Minnesota, public-health officials are advising protesters to get tested for the virus a week or two after the demonstrations, even if they aren’t showing any symptoms.

“There are going to be individuals who are unwitting, potentially exposing others,” said Kris Ehresmann, director of infectious disease for the Minnesota Department of Health. “We know that Covid has an asymptomatic period where people are still infectious, so we are making that assumption that yes, there is likely to be some opportunity for spread.”