By MARC
LIPSITCH and YONATAN
GRAD / APRIL 1, 2020
Imagine you are in a small boat far, far from shore. A surprise
storm capsizes the boat and tosses you into the sea. You try to tame your
panic, somehow find the boat’s flimsy but still floating life raft, and
struggle into it. You catch your breath, look around, and try to think what to
do next. Thinking clearly is hard to do after a near-drowning experience.
You
do, though, realize two important things: First, the raft is saving your life
for the moment and you need to stay in it until you have a better plan. Second,
the raft is not a viable long-term option and you need to get to land.
In
April 2020, the storm is the
Covid-19 pandemic, the life raft is the combination of intense
measures we are using to slow the spread of the virus, and dry land is the end
to the pandemic.
The
U.S. is still in the clambering-into-the-life-raft phase of responding to
Covid-19, and thinking clearly about what to do is still difficult. This
confusion has made it hard to appreciate two facts: One is that social
distancing combined with scaling up testing, production of medical equipment,
and other countermeasures are essential and must be replicated across the
country, intensified, and continued. The other is that if these measures have
the desired effect of reducing the number of new cases accumulating each day,
they provide only a temporary solution.
We still need to find a way to bring the pandemic to a permanent
conclusion.
Several
countries in Asia controlled their epidemics before a majority of the
population was infected. Some, like Taiwan and Singapore, did so by containing infections
from the start. Others, like China and Korea, did so only after large
outbreaks. The control they have reached is only a life raft, not dry land,
because unless there have been extraordinarily high levels of infection that
were so mild as to go unnoticed, most people in these countries remain
susceptible to infection.
Viruses
do not remember they were previously under control and will resurge when
restrictions are lifted. Just look at what happened in 1918, when cities that had
cracked down on the transmission of influenza lifted their restrictions and flu
transmission rose again. Mathematical models of Covid-19 by our group and others that
incorporate these lessons show that, in the short term, social distancing and
other interventions can reduce the impact of the virus. But the same models
show that when these interventions are eased, the problem returns.
Let’s
be clear. With something like Covid-19 there is the first peak, and there’s the
whole epidemic. For the first peak, the evidence so far points to a worrisome
possibility of overwhelming our intensive care units — even with the degree of
social distancing we’ve achieved — as we’re seeing in New York City.
But every bit we slow and flatten the curve will make that less likely and less
dramatic, if and when it happens.
It is very possible that after this first wave subsides, we will
still have a largely susceptible population, though that depends on how well
the social distancing works. Effective treatments and increased ICU capacity
could reduce the demand for critical care, lightning the load on the health
system, but again, these measures only delay things.
If
the SARS-CoV-2 virus has a contagiousness of three, meaning every case infects
three other people, then we won’t get to the end of the epidemic until
two-thirds of the population has become immune by infection or by vaccination.
Successful control of the first peak of infections could leave a majority
(perhaps a large majority) of the U.S. population still susceptible to the
virus.
There
are several broad ideas for how to get to dry land, which is widespread
immunity in the population. But each has enormous problems.
One
way is to let up on social distancing soon and let the epidemic run its course.
That would lead to many deaths and completely overwhelm health care systems around
the country. Another way is to maintain intense social distancing until there
is a vaccine — but the arrival of a vaccine is uncertain and, absent a miracle,
will likely take more than a year. Meanwhile, society and the economy would
suffer.
If
the first wave really is controlled, another option would be to try multiple
rounds of social distancing: instituting it to bring the epidemic under control
then letting up, perhaps only in certain areas, to allow cases to occur and
immunity to accumulate gradually in the population, and then again introducing
another round of social distancing. Our model of this process shows
that it would take multiple rounds and would be challenging to accomplish
without errors that lead to ICU overload. It would also be difficult to
maintain the political and social will to implement this.
The
most ambitious approach would be to intensify social distancing and scale up
testing until we have the ability to know about nearly every case of Covid-19,
trace his or her contacts, and control the spread of the disease one case at a
time. This, though, is hard to envision. Even though Singapore detected the
infection early, Covid-19 has stretched the island’s public health system to
the limits, and our public health system has not had the practice and the
resources devoted to stopping a pandemic that Singapore has invested since it
faced down severe acute respiratory syndrome (SARS)
in 2003. And continued risk of imported cases of Covid-19 from elsewhere in the
world — or even from other parts of the country — would lead us in this best-case
scenario to restrict and intensively screen travelers for an extended period.
As
epidemics and responses to them are local, the scenario in one part of the U.S.
could differ from that in another. A report from the Institute for Disease Modeling suggests
that even Seattle’s relatively prompt response may have only slowed the spread
of the infection and it may see a single-peaked epidemic with much of the
population infected, despite social distancing efforts. If accurate, recently
reported fever data from a
networked thermometer company that illness rates may be coming down, not just
growing more slowly, then we may see a second peak once social distancing
efforts are lifted.
Clearly, we need more
testing to understand each region’s epidemic trajectory.
A vaccine is ultimately our
best hope, but that is in the future — many months away, if not a year or more,
in the rosiest scenarios.
Whatever path we choose —
and it may be a mix of paths in different parts of the country, as the local
epidemics and responses are so varying — we should be working overtime to make
use of the time we buy with social distancing. That means:
·
Building capacity to control transmission by continued social
distancing, massive testing, and meeting the needs of healthcare workers for
personal protective equipment.
·
Investing in efforts to mitigate the impact of Covid-19 by rapidly
finding treatments, increasing health care capacity, and further accelerating
work on a vaccine.
Despite the near-drowning
of hospitals and intensive care units we’ve observed in many countries, and may
soon witness in the U.S., we must think clearly and understand that getting
through the first phase of this pandemic only gets us into the life raft, not
to dry land.
Marc Lipsitch is professor
of epidemiology and director of the Center for Communicable Disease Dynamics at
the Harvard T.H. Chan School of Public Health, where Yonatan Grad is an
assistant professor of immunology and infectious diseases
