Projections Suggest Potential Late May COVID-19 Rebound

The latest data modeling projections by Columbia University Mailman School of Public Health scientists estimate that, nationally, new COVID-19 cases and deaths will rebound in late May, as states ease stay-at-home orders and social contacts increase. By June 1, one projection scenario gives median estimates of 43,353 cases per day and 1,841 deaths per day in the United States. A second scenario with a greater progressive loosening of restrictions projects median estimates of 63,330 cases per day and 2,443 deaths per day by June 1.

In all but two of the 25 states that already have or plan to partially re-open their economies in the coming week, the data model projects substantial increases in COVID-19 cases based on either of two scenarios: (1) a one-time 10 percent increase to the contact rate during the week that the state is scheduled to reopen and (2) a weekly 10 percent increase in contact rates, which represent a progressive loosening of restrictions and increased public confidence and frequenting of businesses. Daily confirmed cases will likely rise more sharply in the second scenario, notably in Texas where they could pass 500 by early June. If stay-at-home orders in these states had been maintained, cases would likely have declined.

The researchers anticipate a rebound in COVID-19 cases approximately two to four weeks after states begin to reopen. “The lag between infection acquisition and case confirmation, coupled with insufficient testing and contact tracing, will mask any rebound and exponential growth of COVID-19 until it is well underway,” says lead researcher Jeffrey Shaman, PhD, professor of environmental health sciences.

The new projections cover the upcoming six weeks and are summarized in an article published on Shaman’s Columbia website. Co-authors include Teresa Yamana, PhD, and Sen Pei, PhD, both research scientists in environmental health sciences. Updated weekly, the projections can also be seen using a mapping tool, a data visualization tool that graph projections over time, and animated maps. Shaman and colleagues are advising and providing projections to the White House Coronavirus Task Force, the U.S. Centers for Disease Control and Prevention, New York City, and various state governments.

“Strong social distancing practices enforced in stores, restaurants, and theaters, as well as increased use of face masks, could offset increases in person-to-person contact. However, it is quite possible that a return to greater activity will reverse some of the gains accrued over the last six weeks, particularly if initial re-openings do not produce an immediate growth of cases and consumer confidence grows,” says Shaman. “Eventually, as individuals and states see a rise in infections and deaths, they may reimplement tighter restrictions on contacts.”

As infections rise where stay-at-home orders are lifted, hospital critical care capacity in those states will be stressed in ways already seen in hard-hit areas like New York City. “We don’t want to re-experience the crippling patient surges, patients who died because hospital volumes were so high, and the utterly tragic loss of healthcare worker lives,” says Charles Branas, PhD, chair of epidemiology, who contributed to the model of hospital capacity.

The 25 states that have eased stay-at-home orders or plan to ease stay-at-home orders, as of May 2: Alabama, Alaska, Colorado, Florida, Georgia, Idaho, Indiana, Iowa, Kansas, Maine, Minnesota, Mississippi, Missouri, Montana, Nebraska, North Dakota, Ohio, Oklahoma, South Carolina, South Dakota, Tennessee, Texas, Utah, West Virginia, and Wyoming.

New York City Findings

New neighborhood-level projections in New York City point to an easing of COVID-19 infections, hospitalizations, and deaths over the next six weeks, including in North Central Queens which has seen the highest numbers in recent weeks. On a per capita level, northern Staten Island and Far Rockaway, Queens, are expected to be most affected in the coming weeks.

The latest projections find that in recent weeks the rate of transmission has sped up in some neighborhoods, likely due to relaxed social distancing. These areas include parts of Staten Island, the Bronx, and Queens.

“Citywide projections assuming a 50 percent increase in the contact rate due to relaxed social distancing show the number of infections in the coming eight weeks could be twice as high as would be seen if the city maintains the current rate of contact,” says Wan Yang, PhD, lead on New York City projections and assistant professor of epidemiology.

About the Model and Its Uncertainties

The researchers use computer models to project the spread of COVID-19 cases by accounting for transmission and case-fatality parameters, population movement, including by commuters, with U.S. Census Bureau data, and other constraints and variables. Updated national projections posted on Github include data on hospitalizations, critical care admissions, and mortality under varying levels of social distancing and hospital surge response. New York City projections are also posted on Github.

The researchers emphasize a number of uncertainties, including the fact that their model may not account for changes in social distancing and contact patterns over the last two weeks. Increased virus transmissibility is only applied to states in which a reopening of the economy has or is slated to occur, not to counties neighboring those states. In addition, the impact of increased activity on contact patterns, the transmission of SARS-CoV-2 and COVID-19 incidence remains highly uncertain, as levels of compliance with social distancing, return to work, and consumer willingness to frequent businesses are unknown.