YSM Issue 94.1

Public Health
SCOPE
However, the 2007 University of
Hong Kong investigation revised the
travel distances of droplets in indoor
environments by modifying the
Wells evaporation-falling curve. The
researchers used mathematical models
to relate droplet travel velocity to the
rate of mass and heat transfer and
droplet displacement. Ultimately, they
found that droplet travel distance was
profoundly affected by compounding
variables such as air currents and relative
humidity, establishing that droplets
from sixty to one hundred μm in size
could travel for more than six meters
in certain humidities if originating at
a velocity of fifty meters per second.
Additional studies conducted in 2014
and 2016 by the Bourouiba Group, which
focuses on research at the interface of
fluid dynamics and epidemiology at the
Massachusetts Institute of Technology,
have speculated that droplets originating
from violent respiratory events
(coughing or sneezing) could travel for
more than seven to eight meters.
Thus, it is challenging to quantify the
scenarios in which COVID-19 transmission
can occur, and varying datasets can make
it impossible to construct adequate safety
guidelines. To complicate matters further,
viral payload within droplets as well as
air pollution levels—pollutants can help
the virus remain suspended in the air—
also affect transmissibility of the disease.
During the COVID-19 pandemic, the
CDC and World Health Organization
(WHO) have set different guidelines on
the distance healthcare workers should
have from patients, at two meters and one
meter, respectively. How did the CDC and
the WHO come up with such guidelines,
and why are they so different?
IMAGE COURTESY OF PIXABAY
The CDC recommends six feet of social
distancing between individuals to limit COVID-19
transmission.
The data informing WHO guidelines
originated from research from the twentieth
century, which measured infection rates from
rhinovirus colds and bacterial meningitis.
This data persisted as a worldwide guideline
for the COVID-19 pandemic.
Yet, the CDC, a United States federal
agency, conducted multiple rounds of
research on viral droplet transmission and
came up with a different set of guidelines.
In 2007, the CDC published a manual
for healthcare workers detailing droplet
transmission rates. They found through
epidemiological and experimental
modeling that there is a high risk of
transmission if one is within a three-foot
radius of the patient, producing similar
results to the research informing WHO
guidelines. However, they noted that
during the 2003 global SARS outbreak,
there were reports of droplets traveling
up to six feet while retaining their
infectious capabilities. As a result, they
established that “it may be prudent to don
a mask when within six to ten feet of the
patient.” Research completed during the
2009 H1N1 flu virus outbreak, however,
revised CDC guidelines such that a “close
contact is defined as working within six
feet of the patient or entering into a small
enclosed airspace shared with the patient.”
This definition has been maintained and
continues to inform American guidelines
during the COVID-19 pandemic.
Yale has also developed its own
guidelines regarding safe practices for
students on campus, from lowering its
student capacity to suggesting guidelines
for social distancing. By limiting
gatherings to no more than ten people,
mandating an hour time limit between
uses of music rooms, and placing indoor
signs marking six-foot distances, Yale has
taken recommendations from the CDC
and State of Connecticut and modified
them to fit a university setting. But Yale
faces a unique challenge: how do you
balance student safety with the creation
of an “authentic” Yale experience?
In an email correspondence, Natenin
Cisse (MY ’22), a Yale Public Health
Education for Peers representative, said:
“There are plenty of signs and stickers
throughout [Yale libraries] to ensure that
people are socially distanced. Library
COVID-19 viral particles.
IMAGE COURTESY OF PIXABAY
workers also monitor the rooms to enforce
social distance. Of course, this isn’t the
same as a usual school year, but going to
the library to study with friends is still
feasible and enjoyable as usual, so this is
one way Yale has effectively preserved our
student experience while also ensuring our
safety.” With their guidelines, Yale seeks to
contain any positive COVID-19 cases and
prevent large, super-spreader events.
Nonetheless, no guidelines can be
completely effective. Due to varying
scientific data and the impossible task
of modelling every droplet transmission
scenario, many regard social distancing
and CDC guidelines to be inadequate.
There is still discussion over whether
or not six feet of social distancing
is enough to prevent COVID-19
transmission. On July 6th, 2020, a
group of 239 scientists from more than
thirty-two countries wrote to the WHO
urging them to expand their guidelines
beyond one to two meters and scale it
up to “several meters, or room scale.”
Although the guidelines were never
changed, it still posed a robust counter
to the magic number “six.” Thus, it is
up to the discretion of the individual
to determine what behaviors they are
comfortable with—even if it means ten
feet between you and your neighbor at
the grocery store—because guidelines
are, after all, only guidelines. ■
The full list of sources for this article
is available at https://medium.com/
the-scope-yale-scientific-magazinesonline-blog
www.yalescientific.org
March 2021 Yale Scientific Magazine 33