Density is not causally linked to Covid-19 infection or death rates, according to a new study of more than 900 U.S. counties from the Johns Hopkins Bloomberg School of Public Health. Shima Hamidi and her coauthors found that, after accounting for various factors like education and race, a higher density of jobs and population leads to lower death rates from the novel coronavirus, likely due to better health-care options and social-distancing practices.
Population size and social connectivity affect infection and mortality rates more than density. Larger metro areas with tightly interwoven economies, societies, and commutes are likelier to see the spread of contagious disease. Not all cities are dense, and how people commute and live within them varies—and those differences matter in a pandemic. As was the case in New York City, a virus in a hyperconnected mega-region can easily jump from an international airport to the city center before fanning out to the suburbs, where travel patterns resemble Pollack paintings more than the stick-figure lines of a subway commute.
The result is that a less-dense county like Westchester in New York can suffer a more intensive outbreak of Covid-19 than Manhattan, the nation’s densest stretch of land. In the New Orleans metro area, the study’s authors find, county density varies far more than infection rates, explaining less than a quarter of the variation in the virus’s spread. An automobile ping-ponging the sick across a large, sprawling metro can be a recipe for disaster. The experience of Asia and Australia seem to confirm density’s weak hold on this pandemic: cities like Taipei, Tokyo, Seoul, and Sydney enjoy greater densities with fewer deaths from Covid-19 than their less-dense peers.
While density intuitively seems correlated with contagion, anyone who has tried talking to strangers on New York City’s subway knows that its riders are well practiced in social distancing. Smartphone data reveal city dwellers were likelier to stay at home and away from others during the pandemic than their suburban or exurban peers. Even when stuck in a cramped city, greater density of people translates into better options for services like home delivery, wider abundance of grocery stores open for more hours, and more choices in health care.
New York City’s experience dramatically illustrates the pandemic’s complexity and many factors that explain its spread. Predominantly minority and poor neighborhoods rife with underlying health conditions—like, say, East New York—proved dramatically more vulnerable to infection and death from Covid-19. Working-class black and Hispanic communities in Queens saw hardly any change in their commuting patterns during the worst of the pandemic and probably suffered for it; whiter neighborhoods in Manhattan and Brooklyn, with more office workers able to work from home, experienced commuting drop-offs of 60 percent or greater. Death rates from Covid-19 in New York City differ by orders of magnitude depending on zip code.
In some neighborhoods, overcrowded housing may play a greater role than density in the spread of Covid-19. Though Johns Hopkins researchers in this instance found “no relationship to the virus rate” in housing with more than one person per room, NYU’s Furman Center showed that overcrowded renters in New York were likelier to contract the virus, and in California, “the hardest hit neighborhoods had three times the rate of overcrowding as the neighborhoods that have largely escaped the virus’s devastation.” Crowded housing also raised mortality rates from Covid-19, according to a study of Massachusetts neighborhoods by Harvard University researchers. Pricey housing is one reason why New York City has more households with roommates than nuclear families, and why untold thousands live together in illegal basement dwellings—both living arrangements that abet disease spread. These are challenges of housing policy as much as public health.
Defending density does not leave cities off the hook. Larger urban areas introduced and spread Covid-19 throughout the world—a reality that has plagued cities throughout history. Viruses are urban devils, after all. This coronavirus came from China to Seattle, and China to Europe to New York City, before spreading more broadly.
The Johns Hopkins study’s authors, primarily urban planners, admit that theirs is only the “first word, not the last” on urbanism’s relationship with Covid-19. More research will need to be done on the pandemic and its complex relationship with density. That hasn’t stopped New York governor Andrew Cuomo from declaring “It’s very simple. It’s about density.” But if recent studies are any guide, it’s increasingly clear that, where Covid-19 is concerned, density is not necessarily destiny.
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