Model highlights problems implementing uniform mitigation strategy

Even a one-week delay in the implementation of social distancing measures would have had a major effect on the total number of Covid-19 infections over time in several regions of the United States, especially New York City, a modeling study of 3 regions in the U.S. has shown.

In a simulation model that represents interactions among people living in the region assessed, implementing social distancing measures one week earlier in New York City could have reduced the number of Covid-19 infections by 80% by the end of May, 2020, Oguzhan Alagoz, PhD, University of Wisconsin-Madison, Madison, Wisconsin and colleagues reported in the Annals of Internal Medicine.

In contrast, a single week’s delay in the implementation of the same social distancing measures could have increased the number of confirmed cases by almost 7-fold again by the end of May, the authors observed.

“The effectiveness of social distancing measures depends on how closely a population follows them and the type of measures that are implemented at different times,” Alagoz and his colleagues pointed out.

“[O]ur model shows that delayed implementation of, low adherence to, and premature easing of social distancing generally resulted in increased cases of Covid-19 in urban areas of the United States,” they concluded.

Simulation Model

The model used to estimate the effect that social networking had on the incidence of Covid-19 infections took into account a number of factors including population density, the daily number of contacts among residents in the absence of social distancing measures and various levels of adherence to those measures.

“Our model, the Covid-19 Agent-Based simulation Model (COVAM), allows transmission from asymptomatic patients, accounts for imported cases during the early days of the pandemic and considers the possibility that some patients with mild to moderate symptoms never receive confirmatory testing for Covid-19,” the authors noted.

Adherence to social distancing measures included in the model served as a proxy for several behaviors that reduce the transmissibility of SARS-CoV-2 including infrequent travel, keeping at least 6 feet apart during person-to-person interactions, frequent handwashing and wearing masks, investigators stressed.

“[C]ompared with 50% adherence, no social distancing other than closing schools increased the total number of cases from 56,433 to 487,501 in NYC (New York City) in just 26 days (by 31 March),” researchers reported.

Furthermore, earlier easing of the social distancing measures would have had “major detrimental effects” on the total number of infections seen in New York—especially when there was a significant decrease in adherence to these measures after their easing.

For example, easing of the measures on June 1, 2020 instead of when they were actually eased on June the 8, 2020, coupled with a decrease in adherence to those social distancing measures of just 5%, would have increased the total number of Covid-19 cases from 224,194 to 230,932 as of the end of July.

“If adherence had decreased by 15 percentage points after social distancing measures were eased on 8 June, the number of cases could have increased from 224,194 to 439,728 by 31 July, showing the importance of personal behaviors that prevent transmission of SARS-CoV-2, such as face mask use after the measures are eased,” the authors emphasized.

Other Regions

The authors applied the same COVAM model to 2 other regions in the U.S.— Dane County in Milwaukee and the Milwaukee metropolitan region, which is approximately 3 times the size of Dane Country.

Modeling results showed that a delay in implementation had a different effect on the number of Covid-19 cases in the Milwaukee metro area compared to Dane County—a sign that the effect of social distancing measures varied even within the same state as they depended upon local levels of both transmission and adherence to safety measures.

For example, implementing social distancing measures one week earlier would have reduced the number of infections by 46% in Dane County and by 52% in the Milwaukee metropolitan area as of May 15, 2020.

“[O]ur model estimated that 70%, 70% and 85% adherence to social distancing measures in Dane County, Milwaukee, and NYC, respectively, would be needed to keep the pandemic in a steady state,” the authors wrote.

“[C]ities and regions should strongly encourage the community to maintain behaviors that reduce the transmissibility of SARS-CoV-2, such as wearing masks,” they said.

Commenting on the findings, Jeffrey Koplan, MD, MPH, Emory University, Atlanta, Georgia and colleagues from the University of Washington in Seattle, pointed out that Alagoz and colleagues make a “strong case” for recognizing the threat of the Covid-19 pandemic outbreak as soon as possible and taking decisive action.

“The findings corroborate the growing scientific consensus that social distancing mandates (for example, limiting the size of group gatherings and closing schools and nonessential businesses) limit community spread of respiratory viruses such as severe acute respiratory syndrome coronavirus 2,” Koplan and colleagues noted.

At the same time, the editorialists were strongly critical of the U.S. federal response to the Covid-19 pandemic.

“Downplaying the severity of Covid-19 as nothing more serious than the common flu is an insult to the 210,000 (plus) grieving families of persons who died so far [from Covid-19] and the many more who have had the illness,” the editorialists stated. “The American public has paid dearly for this recklessness.”

Indeed, Koplan and colleagues predicted that Covid-19 will be the second leading cause of death in the U.S. by the end of 2020, disproportionately affecting Black Americans and other persons of color because they do not have the luxury of working from home as many white Americans do and are thus at a much higher risk of exposure to the virus.

“With mass vaccination months, if not years, away and few effective therapies, the timely use of nonpharmaceutical public health interventions will reduce morbidity and mortality from Covid-19,” Koplan and colleagues wrote.

“Alagoz and colleagues’ study provides an opportunity to pause and asses how modeling can and should inform Covid-19 decision making,” they added.

  1. A simulation model in which the effect of the timing of the introduction and easing social distancing measures was calculated showed both time points had a profound effect on the number of Covid-19 infections in the U.S.
  2. The effect that social distancing measures had on Covid-19 infection rates were highly dependent on both the level of social adherence to and transmission of Covid-19 within that particular region.

Pam Harrison, Contributing Writer, BreakingMED™

Alagoz reported receiving personal fees from Biovector Inc.

Koplan reported receiving “other” from Kaiser Health Plan- Georgia, the Robert Wood Johnson Foundation, and the CDC Foundation.


Cat ID: 190

Topic ID: 79,190,190,926,192,927,150,151,928,925,934