Berks County Medical Society Medical Record Winter 2021 - 16

M e d i c a l R ec o r d F e a t u r e

SARS-CoV-2 Vaccine is here!
by Debra Powell, MD, Chief, Section of Infectious Diseases &
Medical Director, Infection Prevention, Tower Health

THE HEADLINE:
Three million doses of COVID-19 vaccine
were shipped on Sunday morning, 12/13/2020,
from the Pfizer plant is Kalamazoo, Michigan.
This rapid rollout follows the FDA Emergency Use
Authorization issued on Friday, December 11, 2020.

THE BACKGROUND:

in the 50 - 64-year-old age group with 8.6%, and those
over 65 year old age group with 2.5%. Additionally, the
distribution of antibodies was more prevalent in those
who lived in metro areas at 12.3% compared to nonmetro areas of 1.7%.1

WHAT PERCENTAGE OF THE
POPULATION HAS TO BE IMMUNE
TO ACHIEVE HERD-IMMUNITY
FOR SARS-COV-2?

The impact of COVID-19 across the world has
been devastating in terms of morbidity, mortality,
and economic impact. I suspect that all of us have been impacted
either professionally, personally, or both. As of Dec 13, 2020, there
have been more than 72 million cases of COVID-19 worldwide with
over 1.6 million deaths. Within the United States, there have been
over 15 million cases with almost 300,000 deaths. In Berks County,
we have diagnosed over 17,000 cases with 490 deaths. Our hospitals
are surpassing the daily COVID-19 positive inpatient census seen
during the prior spring surge. This exponential increase follows the
Thanksgiving holiday. The national health care system is being taxed
like never before. Today, there are 108,000 hospitalized patients
reported across the country. State governments are issuing increasing
restrictions trying to flatten the curve with limited success.

Herd-immunity refers to the percentage of the population that
has to be immune to decrease the likehood of an infected individual
contacting a susceptible individual to spread the infection. For
most infections, 50-90% of the population needs to be immune to
achieve herd-immunity. The formula for calculating herd-immunity
is 1-1/R0.2 R0 refers to the number of infections caused by one
infected individual. Most studies estimate that R0 for SARS-CoV-2
is between 2 and 3. For SARS-CoV-2, assuming no population
immunity, the herd immunity threshold is predicted to be between
50 - 67% of the population.

In order for the pandemic to end, we have to decrease the
number of infections and decrease the number of infections each
positive case creates. We have a number of tools that we have been
using since March including mask use, social distancing and hand
hygiene. More recently, the US has supported contact tracing with
isolation of positive cases and quarantining exposed individuals.
These measures have been partially effective but require rapid testing,
rapid reporting, and compliance. The most effective and the best
long-term solution is to establish immunity.

Using the above estimate of 60%, for the US to achieve herdimmunity for the 330 million population, 198 million people
would have to become infected and develop antibodies. The WHO
estimates the infection fatality rate for COVID-19 to be 0.5%. For
us to achieve herd-immunity naturally in the US, this would cause
an estimate 990,000 deaths.3 This loss is too large to allow nature to
run its course.

HOW MANY PEOPLE HAVE ANTIBODIES?
Recently published antibody surveillance studies have shown that
the seroprevalence of SARS-CoV-2 antibodies in Pennsylvania as of
September 24, 2020, was 11.1%. The highest prevalence was seen
in the 18 - 49-year-old age group of 14.8%, with lower percentages

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WHY CAN'T WE LET HERD-IMMUNITY
HAPPEN NATURALLY?

VACCINATION UPDATE:
The best method to achieve herd-immunity rapidly is through
vaccination. As of December 13, 2020, there are 15 vaccines in
phase 3 studies. On December 11, the FDA authorized the PfizerBioNTech vaccine for Emergency Use Authorization (EUA) for
individuals over 16 years of age. The Moderna vaccine is under


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Berks County Medical Society Medical Record Winter 2021

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