Coronavirus
Pandemic
Amidst
Uncertainty, Epidemiology Modellers Make The Case For Social
Distancing Measures
Most Dramatic
Strategy Seen As The Only Option
Effectiveness
Still In Doubt
Developments in the
current COVID-19 pandemic are happening rapidly as case counts are
doubling every several days and policy interventions are being
modified to keep pace with new information about how this virus
behaves or is likely to behave.
Modelling
A modelling study
which reportedly had significant influence on decision making about
social distancing measures in Great Britain and the
United States was
released on March 16 by a COVID-19 Response Team at the Imperial
College in London. Entitled “Impact of non-pharmaceutical
interventions (NPIs) to reduce COVID-19 mortality and healthcare
demand”, the paper characterizes the public health threat as “the most
serious seen in a respiratory virus since the 1918 H1N1 influenza
pandemic.” It was authored by Neil Ferguson and 29 co-authors
from the various centers and institutes at the Imperial College.
Unmitigated
Pandemic Impact
Without putting into
place effective control measures, the pandemic is predicted to cause
2.2 million deaths in the US, peaking this coming summer, and about a
quarter of that number (510,000 deaths) in Great Britain, peaking a
bit earlier. Of special concern is that this number of cases creates a
demand for critical care beds that exceeds 30 times the current
maximum bed capacity in both countries.
Mitigation Vs
Suppression
With control measures
possible, the report makes a distinction between mitigation and
suppression strategies. Mitigation seeks to slow but not stop virus
spread in an effort to buy time for the health care system to care for
patients. Suppression seeks to reverse the increasing number of cases
and to keep case numbers low.
Perhaps the most
significant finding in the report, according to the authors, is that
mitigation strategies still result in a need for hospital beds that is
8 times greater than the existing surge capacity. More alarming,
mitigation alone still allows for 250,000 deaths in the UK and 1.1-1.2
million in the US. “We therefore conclude that epidemic suppression is
the only viable strategy at the current time,” says the report, for
countries that can achieve it.
Can it be done?
The feasibility of
such an all-out suppression strategy is very much in question, not
only because of its inherent challenges but because it must be
implemented for a long period of time until a vaccine becomes
available. Otherwise, removing the austere measures would be likely to
produce a rebound in transmission. But even if it succeeds,
suppression may not completely protect the most vulnerable and deaths
could still be high, according to the report.
The authors admit
making their recommendation without consideration of ethical, indirect
adverse health, and economic consequences that might be entailed by a
suppression strategy. Saving lives from coronavirus death is
prioritized above all else.
Proposed
Interventions
Since the feasibility
of effectively implementing suppression strategies remains an open
question, it is important to consider what interventions are involved
in a suppression strategy. According to Ferguson and colleagues,
suppression requires 1) long term sustained social distancing of the
entire population, 2) home isolation of cases and household quarantine
of their family members, and possibly 3) school and university
closures. Under their model, long term sustained social distancing
means that all households reduce contact outside the household,
school, or workplace by 75%. In this scenario, household contact
rates are assumed to increase by 25%.
Conclusion
The authors conclude
that it will be necessary for jurisdictions to layer multiple
interventions and that “The choice of interventions ultimately depends
on the relative feasibility of their implementation and their likely
effectiveness in different social contexts.”
Somber Note
The report ends on a
somber note:
“…it is not at all
certain that suppression will succeed long term; no public health
intervention with such disruptive effects on society has been
previously attempted for such a long duration of time. How populations
and societies will respond remains unclear.”
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