Estimated Mortality Rate (0.4%-0.82%)
Serological studies (aka: antibody tests) are taking place for SARS-CoV-2, and we are beginning to understand the larger picture of this virus. As of May 2020, these studies show that roughly 1% to 7% of the US population was already infected with SARS-CoV-2. Many of these cases were minor or asymptomatic, and they went undetected. Because of the large number of undetected cases, the current mortality rate is estimated to be somewhere around 0.4% to 0.82%, just a bit deadlier than the seasonal flu.
Potential Herd Immunity (60%–80%)
If and only if antibodies guarantee immunity, we will eventually reach some level of herd immunity in the future. Herd immunity is estimated to be somewhere between 60%-80%.
Herd Immunity — Infection vs Vaccination
Herd immunity can be achieved in a couple ways: widespread infection, widespread vaccination, or a combination of the two.
As of July 20, 2020, there is no vaccine available to combat SARS-CoV-2, and that means there is no way to artificially reach herd immunity. If we treat the entire US population as our herd, we could expect 60% to 80% of us to get the virus if no vaccine is found. Like I said before, many of those cases would likely be minor or asymptomatic.
Four Possible Scenarios
With the current information available, I see four possible scenarios. The United States seems to be in scenario 4 (and trying to make scenario 2 & 3 a reality).
- Scenario 1 — Natural Herd Immunity. Estimated 794,400 to 2,171,360 deaths in the United States. No preventative measures taken. Let the virus “run its course” by infecting 60% to 80% of the US population at a fatality rate of 0.4% to 0.82%.
- Scenario 2 — Vaccine. A safe and effective vaccine becomes available. We would artificially reach a level of herd immunity while avoiding the number of deaths as seen in scenario 1.
- Scenario 3 — Treatment. A viable and effective treatment for COVID-19 becomes available. We would reduce the number of deaths as seen in scenario 1.
- Scenario 4 — Slow the Spread. Implement ways to slow the spread of the virus (e.g. masks, social distancing, increased cleaning, contact tracing, testing, quarantine, etc.). Avoid spreading the virus to the most vulnerable. Overall death burden is lessened. Race to find an effective vaccine or treatment.
Unknowns & Other Assumptions
We don’t exactly know how immunity from SARS-CoV-2 works. Would immunity last a lifetime or would it only last a few months? Would a single-dose vaccine work, or would there be a need for booster shots? Can the virus remain dormant within the body and suddenly reactivate later in life, as with chickenpox/shingles?
It’s also an assumption to treat the entire United States as a single herd. In reality, our country is not a homogeneous mixture. We are varied throughout, each state and each county having different characteristics (e.g. age, population density, workforce, schools, etc.). Herd immunity in theory is different than herd immunity in practice.
Another assumption is related to the antibody studies. How accurate are the tests? Are the random samples representative of the population as a whole?
The Fog of War
The “fog of war” is a military saying about the uncertainties for a given situation or military operation. There are many unknowns about this virus, and we are currently operating in that fog. We have to study and learn more about this virus to clear the fog. Continuing efforts like this antibody study will help in our fight against this virus.
Commercial Laboratory Seroprevalence Surveys | Coronavirus | COVID-19 https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/commercial-lab-surveys.html
COVID-19 Antibody Test — How it Works and Who Should Get Tested https://youtu.be/7WuMYXPZc0I
COVID-19 Pandemic Planning Scenarios https://www.cdc.gov/coronavirus/2019-ncov/hcp/planning-scenarios.html
Chickenpox | Monitoring Vaccine Impact | Varicella https://www.cdc.gov/chickenpox/surveillance/monitoring-varicella.html
FastStats — Immunization https://www.cdc.gov/nchs/fastats/immunize.htm
Flu Vaccination Coverage, United States, 2018–19 Influenza Season https://www.cdc.gov/flu/fluvaxview/coverage-1819estimates.htm
Fog of war https://en.wikipedia.org/wiki/Fog_of_war
Herd immunity and COVID-19 (coronavirus): What you need to know https://www.mayoclinic.org/diseases-conditions/coronavirus/in-depth/herd-immunity-and-coronavirus/art-20486808
History and Epidemiology of Global Smallpox Eradication https://stacks.cdc.gov/view/cdc/27929 https://web.archive.org/web/20100127095152/http://emergency.cdc.gov/agent/smallpox/training/overview/pdf/eradicationhistory.pdf
Italy Nears Herd Immunity As Over Half of Its Covid-19 Epicenter’s Population Tested Positive for Antibodies https://www.sciencetimes.com/articles/26009/20200610/over-50-citizens-tested-positive-coronavirus-antibodies-italys-epicenter-what.htm
Pinkbook | Measles | Epidemiology of Vaccine Preventable Diseases https://www.cdc.gov/vaccines/pubs/pinkbook/meas.html
Pinkbook | Varicella | Epidemiology of Vaccine Preventable Diseases https://www.cdc.gov/vaccines/pubs/pinkbook/varicella.html
Poliomyelitis-related case fatality ratio (CFR) during a large outbreak https://idsa.confex.com/idsa/2007/webprogram/Paper24062.html
“When will it be over?”: An introduction to viral reproduction numbers, R0 and Re https://www.cebm.net/covid-19/when-will-it-be-over-an-introduction-to-viral-reproduction-numbers-r0-and-re/