By Daniel Farber Huang
July 10, 2020
A new study suggests an unexpected impact of the Black Lives Matter protests was encouraging multitudes of non-protesters across the U.S. to practice extended physical distancing by staying home during the several days of protest. The proportion of people staying home during the protests was significantly greater than would normally be the case, resulting in an overall temporarily reduced COVID-19 spread around the country, the study found.
On May 25 in Minneapolis, a 46-year-old black man, George Floyd, was killed while being detained by police. He died of asphyxiation as police officer Derek Chauvin kneeled on his neck for eight minutes and 46 seconds. Three other officers stood alongside Chauvin as Floyd died. The incident was recorded by witnesses on their phones, sparking national outrage. Fueled by Floyd’s death as well as other acts of police violence against black people, Black Lives Matter protests were organized across the U.S. that lasted several days.
At times, tens of thousands of people gathered for Black Lives Matter protests as COVID-19 continued to infect the broader population, raising concerns of creating “super spreader” events where large populations of people could become infected.
The National Bureau of Economic Research (NBER) published the working paper study (which has not yet been peer reviewed) in late June. The paper was authored by Dhaval Dave, Economics Professor at Bentley University, Andrew Friedson, Assistant Professor of Economics at University of Colorado Denver, and three other co-authors.
It appears there was no evidence that net COVID-19 cases grew at an unpredicted rate in the weeks following the protests. The researchers found there was modest evidence of a decline in the growth rate of cases.
According to the study, common activities at a protest such as chanting or shouting can promote the spread of respiratory droplets, including those infected with COVID-19. Also, police dispersal tactics such as tear gas or pepper spray promote coughing, which increases the likelihood an infected individual will spread disease. Even with face mask wearing, these types of protest activities would be expected to increase transmission of COVID-19 and other infectious diseases.
Caroline Buckee, an associate professor of epidemiology at the Harvard T.H. Chan School of Public Health said in a June 22 Scientific American interview that most of the Black Lives Matter organizers issued guidelines to the public about recommended use of wearing masks and using social distancing. According to Buckee, other types of recent protests around the country, including anti-lockdown protests, did not encourage participants practice safe behavior.
“I think there's a stark difference between [the Black Lives Matter] protests, where there's an explicit messaging around social distancing and masks, and the anti-lockdown protests, which were explicitly against the public health measures—they encouraged people not to wear masks and not to social distance. That intentional messaging does matter,” Buckee said.
The NBER study suggests that people who did not attend the protests may have chosen to stay away for any number of reasons. Possible factors might have included potential perceived danger if protestors or police acted violently, concern about COVID-19, nighttime curfews, and even being inconvenienced if stores or restaurants or streets might be closed.
Using anonymous cell phone tracking data from Safe Graph Inc., and data on local cases from the Center for Disease Control and Prevention (CDC) the researchers found that cities that had protests saw an increase in social distancing for the overall population relative to cities that did not. Safe Graph gathers anonymous population movement data from nearly 45 million smartphones. The CDC and other COVID-19 researchers have analysed that data to examine social distancing patterns in the U.S.
The study’s researchers analyzed social distancing data for a 30-day period from May 15, 2020 through June 13, 2020, which includes the date of George Floyd’s death (May 25) and the start of protests (May 26).
The researchers believe their study covered a sufficient period of time after the protests to detect changes in COVID-19 infection rates. The median incubation period for COVID-19 is 5.1 days, and 97.5 percent of all infected individuals experience symptoms within 11.5 days. The study’s sample data includes at least 21 days of data following the early protests that took place in 154 cities, and at least 16 days of data for 257 cities, which is longer than the recognized incubation period.
According to the researchers, analysis by other economists found a secondary spread of COVID-19 from spring break attendees after a two-week time horizon, so they believe their data timeframe would capture any Black Lives Matter-related increases in infection.
The researchers focused on 315 of the largest U.S. cities and determined 281 of those cities had Black Lives Matter protests while 34 cities in the sample did not.
The study found that in their sample set nearly 36 percent of the populations remained at home the entire day during the protests. On average, the population stayed at home a median of 12.5 hours per day and for 89.6 percent of the time.
It is possible that the protests caused an increase in COVID-19 spread among attendees, but had little effect across the entire populations where protests occurred. Also, a larger proportion of protesters may be younger individuals who, if infected, may have less severe symptoms and therefore may never get tested and not be counted in official COVID-19 numbers.
Maricopa County, Arizona, however, was an outlier. Otherwise the researchers claim to have found essentially no evidence that Black Lives Matter protests contributed to significant or substantial increases in COVID-19 during the period following the start of the protests.
Larger protests may be perceived to be more disruptive with greater potential for violence, and there are indications that social distancing by non-attendees increases with the larger protests. Media reports of violence associated with the protests, even when in another city, also influence people’s decisions to stay at home.
Although tens of thousands, even hundreds of thousands, of protestors gathered in cities across the country and reduced social distancing during the Black Lives Matter protests, the study suggests that the people choosing to shelter-at-home and avoid public places more than offset those numbers.
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