COVID-19 transmission rebounds quickly after physical distancing rules are relaxed
Massachusetts General Hospital
Looking at data from all 50 states and the District of Columbia, the researchers found a gradual but steady decline in viral transmission rates during the eight weeks immediately preceding relaxation of physical distancing rules.
But almost
immediately after those rules were relaxed, most states reversed course. Eight
weeks after restrictions were lifted or loosened, only nine of 51 still had low
rates of transmission.
"Premature relaxation of social distancing measures undermined the country's ability to control the disease burden associated with COVID-19," writes Alexander C. Tsai, MD, investigator in the Department of Psychiatry at MGH and associate professor of Psychiatry at Harvard Medical School, and colleagues in the journal Clinical Infectious Diseases.
Tsai continues:
"COVID-19 is disproportionately killing so-called essential workers, poorer people, and racialized minorities. In the absence of public health leadership at the federal level, these lockdowns are the best tool we have to slow transmission. But there are real costs to these lockdowns, costs that are again inequitably borne by so-called essential workers, poorer people, and racialized minorities, as well as children in public school programs who disproportionately miss out on school. So local governments need to continue to weigh the risks and benefits of these policies, and not be convinced that once you relax, there is no turning back."
The
investigators previously reported that statewide physical distancing measures
were associated with a reduction in the growth rate of COVID-19 cases in the
U.S. and a short-term reduction in COVID-19 related deaths. Results of that
study were published August 11, 2020 in the open-access journal PLOS
Medicine.
"Essentially
the moment those restrictions were released, those trends reversed," says
Mark J. Siedner, MD, MPH, an investigator in the Division of Infectious
Diseases at MGH, an associate professor of Medicine at Harvard Medical School
(HMS), and senior author of the study.
The
team found that this reversal occurred regardless of the type of restriction:
school closings, restaurant/bar closings, workplace rules, limiting public
events, closing of outdoor recreational facilities, and limits on in-state
travel.
Tsai
and colleagues used data from state governments and third-party sources and
regression modeling to estimate the extent to which relaxation of physical
distancing measures affected control of COVID-19, expressed as a value
represented by the number Rt.
"Rt
is the average number of people each person with COVID-19 will infect,"
Siedner says. "The goal of every public health intervention should be to
get the Rt down to less than one, because if each person on average infects
less than one other person, ultimately the epidemic will be extinguished."
The
data showed that the Rt, averaged across jurisdictions, declined by 0.012 units
per day in the eight weeks leading up to relaxation of restrictions, with 46 of
the 51 jurisdictions studied achieving an Rt below one while the measures were
in place.
After
physical distancing regulations were relaxed, the transmission rate increased
by an average of 0.007 units per day. Eight weeks into the relaxation period,
the average Rt was 1.16, and only nine of the 51 jurisdictions had Rt rates
that remained below one.
Siedner
adds: "The hope was that these measures would lead to sustained changes in
behavior: mask wearing and physical distancing. These data do not give us hope.
Until a vaccine is available, these measures are proving to be the most
effective solutions to contain epidemic hotspots."
Co-authors
of the paper in addition to Tsai and Siedner are Guy Harling, ScD, from
University College London UK and the Africa Health Research Institute in
KwaZulu-Natal, South Africa; and Zahra Reynolds, MPH, and Rebecca F. Gilbert,
BA, from the Medical Practice Evaluation Center at MGH.
