Lancaster Physician Fall 2021 - 17

SUMMER 2021
survival advantage. This might be enhanced
attachment, easier entry into human cells, or
more virus produced per replication cycle, all
of which provides the mutant variant with
an advantage over competing strains. A new
generation of SARS-CoV-2 is " born " every
few minutes in each of the many millions of
infected cells in each of the many millions
of infected COVID-19 patients around the
globe. Each person with COVID-19 becomes
a mutation factory, and a potential source of
a new variant strain.
Genetic variants of SARS-CoV-2 have been
emerging and circulating around the world
since the very beginning of the COVID-19
pandemic. As multiple advantageous mutations
combine to create a variant with a clear
advantage over competing viruses, that new
strain gains ascendency. A variant with a spike
protein mutation that results in a much more
contagious strain, for example, will quickly
out-compete other strains and allow the new
variant to quickly spread through populations
and around the globe. Other types of mutations
can also result in the ability of SARS-CoV-2 to
resist destruction (neutralization) by antibodies.
The evolutionary trend in SARS-CoV-2 has
been both towards more contagious and more
antibody-resistant variants.
Variants have spontaneously arisen in many
areas of the world and have demonstrated
the ability to spread globally. The COVID19
epidemic within the U.S. has revealed a
sequence of gradually more infectious variants
by virtue of cumulative mutations in the spike
attachment protein. The original Wuhan strain
that exited China in December 2019 spread
in the U.S. during the months of March
through May 2020 with a peak incidence
of about 30,000 new cases per day. For each
infected person, two to three others became
infected, a measure known as the reproductive
number. The Wuhan strain was replaced by
a more contagious variant called the G-strain
that arose in Europe in the spring and summer
of that year, causing a rate of infection more
than double that of the Wuhan strain, and
resulting in about 75,000 new cases per day.
The largest jump in case rates occurred during
the winter of 2020-2021. This was the result
of the much more contagious Alpha variant,
which arose in the U.K. and which at one point
reached an average of 250,000 new cases per
day. The Alpha wave in the U.S. lasted from
November 2020 to June of 2021. The Alpha
variant, by virtue of its unique suite of mutations,
was capable of infecting five others for
each person infected. Yet the most recent wave
of COVID-19 nationally, and one we are still
experiencing, is the Delta wave. This variant
is by far the most contagious of all forms of
COVID-19, with 10 new infections caused
by each infected person. Delta is so contagious
that it has completely replaced nearly all other
variants of COVID-19 in the U.S. Delta is
Which variants have been present in the United States (Fig. 1)?
WHO designation
Alpha
Beta
Gamma
Delta
Other names
B.1.1.7
P.1, P.1.1, P.1.2
more contagious than smallpox, whooping
cough, and polio. This high contagion risk is the
result of 18 months of cumulative mutations
and the unrelenting force of viral evolution. We
still do not know the ultimate peak or duration
of the Delta wave, but we do know that where
low vaccination rates and non-compliance with
masking and social distancing combine, this
new variant will thrive.
One of the most intriguing aspects of the
sequential waves of COVID-19 variants across
the globe is not so much why they appear,
but why the waves subside. For example, the
massive COVID-19 outbreak in India (which
also gave rise to the Delta variant) began in
early April 2020 and within a month reached
over 400,000 cases per day. Yet within the
ensuing six weeks it had subsided, long before
a sufficient number of infections to induce
herd immunity had been reached, and at a
time when nationally the vaccination rate was
only three percent. Explosive epidemics of new
variants in other countries and regions have
followed a similar perplexing pattern, with
Country/region of origin
U.K.
B.1.351, B.1.351.2, B.1.351.3 South Africa
Brazil
India
Continued on page 19
LANCASTER 17 PHYSICIAN
B.1.617.2, AY.1, AY.2, AY.3
Lancaster Physician Fall 2021

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