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First published Feb. 13, 2020.
Last updated Apr. 5, 2022, @ 10 am PT.

More than two years into the global COVID-19 pandemic, it appears that the disease is here to stay. Since Feb. 13, 2020, we have posted 148 updates to this Case Study. Some updates were sobering, such as the continuously increasing incidence and mortality numbers and the appearance of new variants; others gave us optimism for the future, like when we saw the scientific community come together to develop novel vaccines.

The last update to this Case Study was on April 5, 2022, and therefore the information below does not reflect the latest state of the pandemic. However, we believe it still provides valuable insights into the vast and rapid scientific knowledge acquired in the past two years.


The novel coronavirus, SARS-CoV-2, is the cause of COVID-19, a severe acute respiratory disease first detected in Wuhan, China. The spread of COVID-19 is a global health risk that has had a significant impact on the economy and the daily lives of people across the globe.

Many therapies with diverse mechanisms of action are currently being tested as treatments for COVID-19. At present, three vaccines, three monoclonal treatments, and one antiviral drug have been Authorized for Emergency use or FDA-approved in the US. Please visit the US FDA Press Announcements page for more information.

Signs & Symptoms

The Centers for Disease Control & Prevention (CDC) believes at this time that symptoms of COVID-19 may appear in as few as two days or as long as 14 after exposure. Individuals with symptoms including, fever, coughing, and shortness of breath should self-isolate and seek COIVD-19 diagnostic and medical advice.1,2 The clinical spectrum of COVID-19 ranges from mild, cold-like symptoms to severe pneumonia, respiratory failure, and in some cases, death.2

Image Reference1
Anyone can be infected by the virus that causes COVID-19, but certain populations appear to be more vulnerable to severe infection: recent evidence suggests that older individuals and those with underlying medical conditions are more likely to experience complications or hospitalization.2
Spread of Infection

The WHO has designated the outbreak a global health emergency.3 As of Apr. 5, there have been 482,400,945 confirmed COVID-19 cases (up 15,159,272 from Mar. 21). Of the total cases, 154,464,736 individuals have recovered, and 6,128,212 have died (up 58,627 from Mar. 21), of which 977,913 are from the U.S. (up 7,308 from Mar. 21).

The case fatality ratio (CFR) measures the proportion of deaths among identified confirmed cases. The relative risk of mortality for different groups of people and countries helps guide resource allocation and policy decisions. The level of transmission in a population may be underestimated if individuals with mild or no symptoms are missing from the data or if under-served groups have decreased access to health care or testing.4

the spread of Infection: U.S. Status Report

COVID-19 cases have been reported in all 50 states, with more than 50,000 cases reported in almost every state. Despite these guidelines, COVID-19 cases are surging throughout the southern and western United States. Despite social distancing guidelines and orders to wear masks in public places to prevent community spread, COVID-19 cases are surging across the United States. Many states, particularly in the Midwest, are reporting record numbers of daily cases.

On Mar. 11, 2020, the WHO Director-General announced that COVID-19 can be characterized as a pandemic.   On Feb. 28, 2020, the WHO raised the Global Risk Assessment level for COVID-19 from high to very high.3   Person-to-person spread (or community spread) has since occurred in countries all over the world.
Anatomy of SARS-CoV-2

From the beginning of the COVID-19 outbreak, the combination of many expedited studies has revealed an unprecedented amount of information for a new disease, including the causative virus (SARS-CoV-2), its genetic sequence, PCR assays, and serological analyses. Efforts are rapidly ongoing with the aim of quickly designing effective treatments, such as a vaccine or antiviral drug.

SARS-CoV-2 Mechanism of Action

Once in the body, SARS-CoV-2 recognizes and attaches to a transmembrane protein called ACE2 found mainly on cells that line our airways. The effectiveness of SARS-CoV-2 in triggering respiratory disease may be due to the evolved structure of the Spike (S) protein, which contains the receptor-binding domain for ACE2 and creates the virus’s recognizable ‘crown’ shape. After binding to an ACE2 homodimer, the virus enters the cell through a process called receptor-mediated endocytosis. Inside the cell, the virus releases its RNA and takes advantage of the host cell’s machinery, allowing it to reproduce, escape, and continue infecting human tissue.

Image Reference5
The situation in Numbers:
How COVID-19 Compares to Other Outbreaks

As more cases emerge, medical professionals and researchers have been able to identify distinguishing traits of COVID-19. Here is a look at other notable viral diseases to show how COVID-19 compares.

Covid-19 Vaccines & variants:
What We Know & What We’re Still Learning

As more and more people are getting vaccinated, public health recommendations are being updated to reflect the new situation. As of May 13, 2021, the CDC’s official guidelines for the U.S. stated that fully vaccinated people no longer need to wear a mask or physically distance in most settings. These updates are a result of the high efficiency of the EUA COVID-19 vaccines and a growing body of evidence that fully vaccinated people are less likely to have an asymptomatic infection or transmit SARS-CoV-2 to others.20

What We Know

All EUA and FDA-approved COVID-19 vaccines currently being distributed are highly effective in preventing COVID-19. In international, randomized, placebo-controlled studies, the Pfizer-BioNTech and Moderna COVID-19 Vaccines were 95% and 94.1% effective in preventing COVID-19 disease.21,22 The Janssen vaccine was 77% effective in preventing severe/critical COVID-19 occurring at least 14 days after vaccination and 85% effective in preventing severe/critical COVID-19 occurring at least 28 days after vaccination.23

What we’re still learning

A growing body of evidence suggests that fully vaccinated people are less likely to have an asymptomatic infection and potentially less likely to transmit SARS-CoV-2. In addition, preliminary studies show some protection against emerging variants of concern (VOC), most notably the Delta Variant (B.1.617, originally identified in India), which shows increased transmissibility and reduced neutralizing antibody response and is currently the main variant circulating in the United States;24 and the Omicron Variant (B.1.1.529, originally identified in South-Africa), which is believed to spread more easily than the original SARS-CoV-2 virus.25

Preventative measures such as mask use and social distancing continue to be important and are still recommended in public indoor spaces for both vaccinated and unvaccinated individuals.20

  1. Coronavirus Disease 2019 (COVID-19) – Symptoms. Centers for Disease Control and Prevention. Published April 27, 2020. Accessed April 28, 2020.
    1. CDC. Coronavirus Disease 2019 (COVID-19). Centers for Disease Control and Prevention. Published February 11, 2020. Accessed September 27, 2020.
    2. Coronavirus disease (COVID-19) – World Health Organization. Accessed September 15, 2020.
    3. Chen N, Zhou M, Dong X, et al. Epidemiological and clinical characteristics of 99 cases of 2019 novel coronavirus pneumonia in Wuhan, China: a descriptive study. The Lancet. 2020;395(10223):507-513. doi:10.1016/S0140-6736(20)30211-7
    4. Zhao Y, Zhao Z, Wang Y, Zhou Y, Ma Y, Zuo W. Single-cell RNA expression profiling of ACE2, the putative receptor of Wuhan 2019-nCov. bioRxiv. Published online January 26, 2020:2020.01.26.919985. doi:10.1101/2020.01.26.919985
    5. Branswell H. The Coronavirus Questions That Scientists Are Racing to Answer. Scientific American. Accessed April 9, 2020.
    6. Leung G. Opinion | The Urgent Questions Scientists Are Asking About Coronavirus. The New York Times. Published February 10, 2020. Accessed April 9, 2020.
    7. Coronavirus Disease 2019 (COVID-19) – Transmission. Centers for Disease Control and Prevention. Published April 2, 2020. Accessed April 9, 2020.
    8. Zhao S, Ran J, Musa SS, et al. Preliminary estimation of the basic reproduction number of novel coronavirus (2019-nCoV) in China, from 2019 to 2020: A data-driven analysis in the early phase of the outbreak. bioRxiv. Published online January 24, 2020:2020.01.23.916395. doi:10.1101/2020.01.23.916395
    9. WHO | Cumulative Number of Reported Probable Cases of Severe Acute Respiratory Syndrome (SARS). WHO. Accessed April 9, 2020.
    10. Types of Influenza Viruses. Centers for Disease Control and Prevention. Published November 18, 2019. Accessed April 9, 2020.
    11. Weekly U.S. Influenza Surveillance Report | CDC. Accessed April 9, 2020.
    12. Biggerstaff M, Cauchemez S, Reed C, Gambhir M, Finelli L. Estimates of the reproduction number for seasonal, pandemic, and zoonotic influenza: a systematic review of the literature. BMC Infect Dis. 2014;14(1):480. doi:10.1186/1471-2334-14-480
    13. Fraser C, Cummings DAT, Klinkenberg D, Burke DS, Ferguson NM. Influenza Transmission in Households During the 1918 Pandemic. Am J Epidemiol. 2011;174(5):505-514. doi:10.1093/aje/kwr122
    14. Morens DM, Fauci AS. The 1918 Influenza Pandemic: Insights for the 21st Century. J Infect Dis. 2007;195(7):1018-1028. doi:10.1086/511989
    15. Lessler J, Reich NG, Brookmeyer R, Perl TM, Nelson KE, Cummings DA. Incubation periods of acute respiratory viral infections: a systematic review. Lancet Infectious Diseases. 2009;9(5):291-300. doi:10.1016/S1473-3099(09)70069-6
    16. Taubenberger JK, Baltimore D, Doherty PC, et al. Reconstruction of the 1918 Influenza Virus: Unexpected Rewards from the Past. mBio. 2012;3(5). doi:10.1128/mBio.00201-12
    17. 1918 Pandemic (H1N1 virus) | Pandemic Influenza (Flu) | CDC. Published March 22, 2020. Accessed April 9, 2020.
    18. History of 1918 Flu Pandemic | Pandemic Influenza (Flu) | CDC. Published January 22, 2019. Accessed April 9, 2020.
    19. COVID-19 Vaccination. Centers for Disease Control and Prevention. Published September 1, 2021. Accessed September 3, 2021.
    20. Office of the. FDA Takes Key Action in Fight Against COVID-19 By Issuing Emergency Use Authorization for First COVID-19 Vaccine. FDA. Published December 14, 2020. Accessed September 3, 2021.
    21. FDA Takes Additional Action in Fight Against COVID-19 By Issuing Emergency Use Authorization for Second COVID-19 Vaccine. FDA. Published December 21, 2020. Accessed September 3, 2021.
    22. Commissioner O of the. FDA Issues Emergency Use Authorization for Third COVID-19 Vaccine. FDA. Published March 2, 2021. Accessed March 16, 2021.
    23. CDC. Delta Variant: What We Know About the Science. Centers for Disease Control and Prevention. Published February 11, 2020. Accessed November 1, 2021.
    24. CDC. Omicron Variant: What You Need to Know. Centers for Disease Control and Prevention. Published December 6, 2021. Accessed December 6, 2021.

The contents of this Case Study, including scientific visualizations, tables, and visual plots, are © 2020 Cognition Studio Inc, all rights reserved. The content of this Case Study is provided to the public strictly for educational purposes. The Case Study relies on publicly available data from multiple sources that do not always agree. As a result of this, Cognition Studio disclaims any representations and warranties concerning the Case Study’s accuracy. Reliance on the Case Study for medical guidance or use of the Case Study for commercial use is strictly prohibited.


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