US distancing measures stabilized but did not reduce SARS-CoV-2 spread
Results of a new study indicate that physical distancing measures in the United States have stabilized, but not reduced, the spread of the pathogen that causes coronavirus disease 19 (COVID-19).
A study published in preprint has suggested that the spread of COVID-19 in the U.S. has stabilized following the implementation of physical distancing measures. The researchers emphasize, however, that the rate of new infections has not been reduced.
It is important to note that this study has not yet been peer-reviewed, so its findings need to be taken with caution. It has been published on the medRxiv server.
Nonetheless, the findings may spur further research into the effects of various government interventions in response to the pandemic and help inform policy going forward.
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Following the sudden emergence and rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), governments across the world have implemented physical distancing measures to help curb the transmission of the pathogen, which causes COVID-19.
Scientific modeling of the effects of different responses to the pandemic has found that widespread physical distancing is likely to be the most effective response, reducing the pressure on public health systems.
However, until now, there has not been enough time since the implementation of physical distancing to analyze its real-world effects.
Given the unprecedented disruption that these distancing measures cause, understanding how they work in practice is important.
It may also give policymakers some clues as to how to respond to the next phase of the virus, as governments throughout the world begin to relax physical distancing measures.
The study involved a statistical analysis drawing on data from every state in the U.S. and the District of Columbia.
It was conducted by the newly set-up Greater Data Science Cooperative Institute, a joint venture between Cornell University and the University of Rochester, both in New York. The institute focuses on using data science to help solve problems in health and medicine.
According to David Matteson, Ph.D. — an associate professor of statistics at Cornell, co-author of the present study, and principal investigator at the data science venture — “Our institute primarily focuses on the mathematical foundations of data science, but we study those to see them have applications in the real world.”
“This was a time where the methodology we’d worked on was directly applicable to this situation. Early in a crisis like this, raw and messy data is maybe the most informative thing that we have.”
Infections stabilized but not reduced
The study found that prior to physical distancing measures being introduced, every 3.31 days, on average, the number of new SARS-CoV-2 infections was doubling.
To arrive at this figure, the authors determined the values for each state and calculated an average. As they note in their paper, “The average of the pre-intervention doubling-rate point estimates across the states was 0.302 days−1, meaning that the number of new infections per day was doubling every 3.31 days.”
After physical distancing measures came into effect, this average rate of infection dropped to doubling every 100 days, demonstrating that physical distancing was clearly having a significant effect on the spread of the virus.
However, while distancing significantly slowed the rate of infection, it was not enough to reduce it to the point at which the number of new daily infections decreased.
As the authors of the study note, this has implications for the relaxing of physical distancing measures.
According to co-author Prof. Aaron Wagner, of the School of Electrical and Computer Engineering at Cornell University, “All the distancing was clearly helping, but it merely stabilized the process.”
“When you’re on a plateau and you start relaxing [physical] distancing, you expect the number of new infections to start accelerating. The virus probably won’t spread as fast as it did pre-intervention, but you expect it to accelerate nonetheless.”
– Prof. Aaron Wagner
“Our findings don’t show much rationale for substantial relaxation of [physical] distancing in the absence of other measures. We don’t have a lot of wiggle room.”
According to the study, other factors may also affect the rate of infection.
These include rigorous contact tracing — which involves healthcare workers identifying and quarantining people known to have come into contact with a person who has COVID-19 — and increased testing to identify who has already had the infection and may, therefore, have developed some immunity to it.
However, until these policies become widespread and the rate of infection starts to decrease — the authors warn — any relaxing of physical distancing is likely to increase the risk of a new rise in infection rates.
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