A new investigation by doctors at the Massachusetts General Hospital (MGH) has shown that physical and social distancing orders issued by the United States government at the beginning of the coronavirus pandemic between March 10 and 25, significantly slowed the epidemic, which led to an estimated reduction of more than 600,000 cases of Covid-19 in the following three weeks, as published in the journal ‘PLOS Medicine’.
“Many have strongly suspected that physical distancing policies helped disrupt Covid-19 transmission during the early days of the epidemic in the United States,” says Mark J. Siedner, infectious disease physician at MGH, associate professor of medicine at Harvard Medical School and a co-author of the research. “This study adds clear evidence to support those suspicions.”
“The results show that the timing of government-issued orders was strongly correlated with reductions in both cases and deaths. In short, these measures work, and lawmakers should use them as an arrow in their quivers to overcome local epidemics in which they do not respond to containment measures,” he says.
The MGH researchers, in collaboration with colleagues from University College London, Harvard TH Chan School of Public Health and the Perelman School of Medicine at the University of Pennsylvania, analyzed data from the first five months of the Covid-19 epidemic in the U.S.
They collected data on government-issued orders for physical distancing measures across the state and compared changes in Covid-19 cases and deaths attributed to the virus in states that implemented physical distancing measures before and after its implementation.
The results show that the average daily rate of growth of COVID-19 cases began to decline approximately one incubation period (that is, four days) after the implementation of the first physical distancing measures across the state.
The time period required for the number of cases to double (epidemic doubling time) increased from approximately four days to eight days in the three weeks after implementation.
These findings are consistent with other recently published works. What is novel is that the researchers found that the average daily death rate attributed to Covid-19 also began to decline after the implementation of physical distancing measures, which had not been analyzed before this study.
The study looked at a wide range of measures, including school and business closures, restrictions on public gatherings, and shelter-in-place orders. Most combinations of these orders appear to have similar beneficial effects.
Because the different types of physical distancing measures were generally implemented in close temporal proximity to each other, the research team was unable to determine specifically which types of physical distancing measures were most effective.
The model findings suggest that statewide measures of physical distancing reduced the total number of reported Covid-19 cases by approximately 1,600 cases per week after implementation and, due to exponential growth in the spread, by approximately 621,000 cases in three weeks after implementation.
“The findings show that the physical distancing measures slowed the growth of the Covid-19 epidemic and saved lives, and also gave our healthcare leaders some time to strengthen their scaling capacity to deal with the epidemic,” highlights lead author Alexander C. Tsai, MGH psychiatrist and associate professor of psychiatry at Harvard Medical School.
However, he regrets that “unfortunately, the national response has largely abdicated the responsibilities of planning a coordinated response, so we probably could have done more sooner. This means that much of the time before these measures were implemented premises were simply wasted,” he says.
For his part, Siedner adds that “this is a case in which past success does not predict future control. The growth of COVID-19 cases appears to be trending upward in many states across the country, including Massachusetts. If containment and more conservative measures fail, we must be prepared for slow or reversed reopening efforts,” he warns. “Until a vaccine is available and equitably widely deployed, we have few other options. Fortunately, our data show these measures work, if we have the means to use them.”