What is Coronavirus (COVID-19)?

Author Chandana Balasubramanian , 18-Jan-2022

COVID-19 is an infectious disease caused by the Coronavirus SARS-CoV-2. First identified in December of 2019, COVID-19 outbreaks turned into a full-fledged pandemic, infecting 500 million people worldwide with over six million deaths [1]. The term COVID-19 is an acronym for ‘Coronavirus Disease of 2019’ — given by the World Health Organization (WHO). 

How is the Disease Transmitted?


The SARS-Cov-2 virus spreads from one infected person to another through droplets in the air. When someone who is infected coughs, sneezes, talks, sings or breathes in close proximity to other people, there is a higher potential for disease transmission. When indoors, smaller particles can linger in the air longer, spread across long distances, and infect others. 


COVID-19 can spread through symptomatic, asymptomatic, and pre-symptomatic individuals, so the disease spreads so fast. About 30% of the infected patients, known as cases, are asymptomatic, and some may be “pre-symptomatic, which means they were initially asymptomatic but developed symptoms later [4]. During the COVID  pandemic, many governments initiated contact tracing protocols to help curb the spread of the virus.

Symptoms of Coronavirus


A person infected with Coronavirus can infect others up to two days before symptoms and remain contagious for ten days or more [5]. 97% percent of those infected show symptoms within 11.5 days [7] and the average incubation period is estimated to be five days. Variants like Delta and Omicron have shorter incubation periods (4 and 3 days, respectively) as they spread faster within the body [8][9]. The most common COVID symptoms are: 

  • Fever
  • Chills
  • Breathing difficulties
  • Body aches 
  • Fatigue
  • Loss of smell or taste 
  • Cough and sore throat 
  • Runny nose and congestion 
  • Diarrhea [6]

Brief History of Coronaviruses


The family of Coronaviruses is, in fact, very common. Many may not know that a form of Coronavirus causes even the common cold. It is named after the crown-like appearance of the spike proteins that occupy the virus’s surface (Corona is Spanish for crown). The first Coronavirus was discovered in 1965, and more forms of coronavirus infections have been detected in humans and animals over the decades. Over the last two decades, three types of Coronavirus have proved to be quite deadly:

  • In 2002, SARS (Severe Acute Respiratory Syndrome) emerged in Southern China and spread to 28 countries infecting 8,000 people and causing 774 fatalities [2].
  • In 2012, MERS (Middle Eastern Respiratory Syndrome) emerged in Saudi Arabia. There were 2,500 cases and 890 fatalities. Though less contagious than SARS, it proved more deadly. Apart from respiratory failure, it caused kidney failures as well [3]
  • The 2019 SARS-CoV-2 coronavirus has proved to be more destructive than the SARS and MERS outbreaks of 2002 and 2012.

Epidemiology of the Pandemic

COVID outbreaks map 2019 to April 2022.

COVID outbreaks map (sometimes also known as a hot spots map) from 2019 to April 2022. 

COVID-19 variants: Delta and Omicron

Like other viruses, SARS-CoV-2 has several mutations, including the Alpha, Beta, Gamma, Delta, and Omicron variants. The Alpha, Beta, and Gamma strains originated in Britain, South Africa, and Brazil. 

The Delta variant

The Delta strain (B.1.617.2) of SARS-CoV-2 is a deadly variant that first appeared in India in December 2020. It spread faster than the Alpha variant and was 50% more contagious than the original SARS-CoV-2 virus. Through the spring and summer of 2021, the Delta variant accounted for the majority of the infections worldwide. For example, as early as April 2021, Delta accounted for 99 percent of the cases in the US [17].

The Omicron variant

The  Omicron variant was first detected in November 2021, and it has three sub-variants, BA.1, BA.1.1, and BA.2. The Omicron variant is more transmissible compared to the Delta. Because of this, there was a considerable spike in cases in early 2022 in several countries, including the United States and China. Fortunately, those infected with the Omicron variant showed much milder symptoms. More research is needed to know if this is due to the nature of the sub-variant or because many people were fully vaccinated, and some even had a booster dose by the time the Omicron variant and subvariants hit.

While the vaccines may have helped slow the spread of the virus, managing the waves of infections continues to pose global challenges, a full three and a half years after the SARS-CoV-2 virus was first discovered.

GIDEON’s COVID-19 Global Status eBook offers a detailed account of the virus, descriptive epidemiology, distribution map, global status, etc.


Biology: How does the SARS-CoV-2 virus infect humans?


The virus enters the human body (or another host) through the nose or mouth. The virus contains ribonucleic acid (RNA) surrounded by a protective layer. This layer has spike proteins on its surface that bind to receptors on host cells called ACE2. After this binding, the virus fuses with human (host) cells, releases its genetic material, and begins replicating. A healthy immune system responds to viruses or bacteria (or vaccines) by producing antibodies against one or more components of the virus or bacteria. With COVID-19, the immune system immediately recognizes the spike proteins, and it starts to produce antibodies. Mutations occur when the virus responds by creating different spike proteins to evade the antibodies. When researchers do genome sequencing, they pay particular attention to the spike proteins [7]. Knowing this has helped with the response to the total cases trend and led to improved guidance for drug research, among other things related to COVID.

What Types of Populations are Most at Risk?

The CDC identifies these three categories of people most at risk of getting COVID:

  • older people,
  • people with medical conditions and/or
  • pregnant and recently pregnant women [10]


In the US, over 81 percent of deaths from Coronavirus are from people 65 and older. In other words, compared to patients aged 18-29 years, patients who were:

  • 65 to 74 years old are 65 times more likely to die from COVID
  • 76-84 are 140 times more likely to die from COVID, and 
  • 85-94 are 340 times more likely to die from COVID [11].


Many health conditions may make people more susceptible to a severe COVID-19 infection. People with lung infections are particularly vulnerable because Coronaviruses primarily target the respiratory system. These conditions include asthma, COPD (chronic obstructive pulmonary disease), and cystic fibrosis. Other medical conditions that may compromise an individual’s immunity are major surgery, heart or kidney diseases, obesity, diabetes, cancer, and mental health conditions [12][13].


Socioeconomic factors can also affect populations at risk, including: 

  • Race/ethnicity
  • Gender
  • Use of certain medications
  • Poverty and crowding
  • Certain occupations [12]


COVID-19 is diagnosed using several types of testing. The positive test rate from these tests depends on a variety of information, but regardless, they can help discover average daily cases and deaths related to the illness. The most widely-used tests are: 

RT-PCR Tests

RT-PCR tests (Reverse Transcription Polymerase Chain Reaction) are the most widely-used molecular tests to detect the presence of the SARS-CoV-19 virus. These tests are done by taking nasal and throat swabs. The PCR test amplifies the RNA obtained from an infected individual’s specimen and converts it into deoxyribonucleic acid (DNA). The process is repeated until SARS-CoV-2 is detected (if present). 

Rapid Antigen Test

An antigen test is another form of molecular test used to detect SARS-CoV2. It delivers results faster than the RT-PCR but may not be as accurate. It tests an individual’s nasal and throat swabs to identify protein fragments (antigens) on the virus’s surface. The technology used is similar to that used in rapid pregnancy tests. False negatives are greater with the antigen test, but they are commonly used as at-home tests or in airports and other locations because they are fast and convenient. These also can help public response to infection since they can let individuals know sooner if they have the disease. On the other side, sometimes, this can make the opportunity to view total cases a little skewed for professionals as reporting probable cases is less likely by the public. As a result, some testing groups actually have opted for a digital test that will submit unidentified results to public health officials in local areas so that they can prepare a better response and perform sound data collection.

Note: An antibody test is not a diagnostic test for COVID-19 because it does not detect the presence of SARS-CoV-2. 



Treatment for COVID-19 depends on the severity of the infection—the WHO offers a classification for healthcare professionals to categorize and treat patients [16]. 

  • Critical Condition
    • patients suffering from acute respiratory distress syndrome (ARDS), sepsis, and septic shock are generally deemed ‘Critical COVID’ condition. Treatment includes the provision of invasive or non-invasive mechanical ventilators and vasopressor therapy.
  • Severe Condition
    • patients with oxygen saturation < 90%, or signs of pneumonia or other signs of severe respiratory distress such as respiratory rates >30 breaths a minute, may be considered in ‘severe COVID -19’ condition.


For patients with severe or critical COVID-19, the WHO recommends:

  • systemic corticosteroids;
  • interleukin-6 (IL-6) receptor blockers (tocilizumab or sarilumab), in combination with corticosteroids;
  • baricitinib as an alternative to IL-6 receptor blockers, in combination with corticosteroids.


Please refer to the WHO therapeutics and living guidelines or the NIH treatment guidelines for an updated list. 

  • Non-severe Condition
    • All COVID-19 patients, other than those with severe or critical symptoms, fall under non-severe COVID-19.


It is helpful to remember that 81% of those infected with COVID experience mild symptoms and don’t need hospitalization [11]. They can be treated by their physician at home, monitoring for any signs of worsening symptoms, including oxygen saturation rates. The main goals of treatment are:

  • to control or slow the virus,
  • reduce an overactive immune response that may worsen the disease, and
  • manage any other health complications. [18]



The best precaution that an individual can take against COVID-19 is to minimize contact with people who may be infected. If contact cannot be avoided, it must be limited as possible. Practicing good hygiene habits is essential. These include: 


Other precautions to lower the risk of getting a COVID infection are avoiding travel and crowded places, staying home if unwell, and coughing into your elbow or a tissue. 


COVID-19 vaccines do not prevent infections from SARS-CoV-2 but are designed to lower the risk of severe disease and hospitalizations. There are a variety of vaccines developed and distributed around the world. Check out the WHO vaccine tracker for a complete and updated list of approved vaccines

Reviews and Meta-analyses …of Meta-analyses and Reviews… of COVID

The following excerpt was written on January 6th by Dr. Stephen Berger.

This morning, COVID-19  –  a disease that has existed for only two years – is cited by PubMed in 213,184 publications.  Influenza and malaria appear in “only” 143,331 and 103,650 titles, respectively.  One recent paper described the clinical features of 73 patients treated in Shenzhen, a city located more than 1,000 kilometers from Wuhan. [1]  The study was performed in 2019 but was published only this week – adding to 1,615 case studies from China (849 from the United States, 277 from Turkey, four from Bahrain, two from Macao, and one from Andorra….).

Much of the literature has become repetitive, contradictory, and tiresome.  Case series and prevalence data are limited to a single hospital, school, city, time frame, or demographic group. The nature of the publishing cycle guarantees that most studies that appear today will be irrelevant and obsolete by next month.

Predictably, a growing number of publications now examine these trends through meta-analysis and systematic review. The reviews themselves cover many thousands of individual surveys and case series.   For example, this is a link to a status report in the United States – one of over 200 similar country-specific notes in GIDEON.

 Full text and linked references are available



Not since the Spanish Flu pandemic of 1918 has a virus spread with speed and tenacity worldwide. The responses to the SARS-Cov-2 virus saw excellent cooperation among countries, governments, the pharmaceutical industry, and the research community to develop and distribute vaccines worldwide. Billions of vaccine doses have been administered to people worldwide to help curb the spread of the virus. Since the COVID-19 virus is relatively new, there is an intense need for more research on the virus, epidemiology, and its short-term and long-term effects on the body.  Clinicians, scientists, and public health officials can work together to help:  

  • Develop more effective vaccines, 
  • Combat the long-term effects of COVID-19,
  • Create consistent treatment regimens, and
  • Limit the spread and severity of the virus. 


The GIDEON COVID-19 ebook is a comprehensive resource to help accelerate COVID research for scientists, academicians, clinicians, epidemiologists, and public health officials. 


[1] WHO Coronavirus (COVID-19) dashboard,” [Online]. 

[2] SARS,”, 31-Mar-2022. [Online]. 

[3] CSR, “MERS outbreaks,” World Health Organization – Regional Office for the Eastern Mediterranean. [Online]. 

[4]CDC, “COVID-19 Pandemic Planning Scenarios,” Centers for Disease Control and Prevention, 03-Apr-2022. [Online]. 

[5] “If you’ve been exposed to the coronavirus,” Harvard Health, 12-Apr-2022. [Online]

[6] CDC, “Symptoms of COVID-19,” Centers for Disease Control and Prevention, 04-Apr-2022. [Online] 

[7].Lauer, S. A., Grantz, K. H., Bi, Q., Jones, F. K., Zheng, Q., Meredith, H. R., Azman, A. S., Reich, N. G., & Lessler, J. (2020). The incubation period of Coronavirus disease 2019 (COVID-19) from publicly reported confirmed cases: Estimation and applicationAnnals of Internal Medicine172(9), 577–582.

[8] .Wang, Y., Chen, R., Hu, F., Lan, Y., Yang, Z., Zhan, C., Shi, J., Deng, X., Jiang, M., Zhong, S., Liao, B., Deng, K., Tang, J., Guo, L., Jiang, M., Fan, Q., Li, M., Liu, J., Shi, Y., … Tang, X. (2021). Transmission, viral kinetics and clinical characteristics of the emergent SARS-CoV-2 Delta VOC in Guangzhou, ChinaEClinicalMedicine40(101129), 101129. 

[9] L. Jansen et al., “Investigation of a SARS-CoV-2 B.1.1.529 (Omicron) variant cluster – Nebraska, November-December 2021,” MMWR Morb. Mortal. Wkly. Rep., vol. 70, no. 5152, pp. 1782–1784, 2021

[10]CDC, “COVID-19 information for specific groups of people,Centers for Disease Control and Prevention, 30-Mar-2022. [Online]

[11] CDC, “Risk for COVID-19 infection, hospitalization, and death by age group,” Centers for Disease Control and Prevention, 28-Mar-2022. [Online]

[12] CDC, “Assessing risk factors for severe COVID-19 illness,” Centers for Disease Control and Prevention, 26-Nov-2021. [Online]

[13] “COVID-19: Who’s at higher risk of serious symptoms?,” Mayo Clinic, 01-Mar-2022. [Online]

[14] R. H. Shmerling, “Which test is best for COVID-19?,Harvard Health, 10-Aug-2020. [Online]

[15] “PCR test for COVID-19: What it is, how it’s done, what the results mean,” Cleveland Clinic. [Online]

[16]MAGICapp,” [Online]

[17] Katella, K. (2022, March 1). 5 things to know about the Delta variant. Yale Medicine.  

[18] [Online]

[19]The fastest vaccine in history,” [Online]

[20]Office of the Commissioner, “COVID-19 vaccines,” U.S. Food and Drug Administration, 18-Apr-2022. [Online]. 

Chandana Balasubramanian

Chandana Balasubramanian is an experienced healthcare executive who writes on the intersection of healthcare and technology. She is the President of Global Insight Advisory Network, and has a Masters degree in Biomedical Engineering from the University of Wisconsin-Madison, USA.

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