Disease & Vaccine Information

What is SARS-Coronavirus-2 and COVID-19 (SARS-CoV-2)?

Updated September 07, 2022


Coronaviruses come from a large family of viruses that are known to cause infections like the common cold. Named for their crown-like spiked surfaces, these viruses are further classified into four additional sub-groups known as alpha, beta, delta, and gamma.

First identified in the mid-1960’s, there are seven known coronaviruses that can cause illness in humans. The four common coronaviruses circulating among humans are:1

  • 229E (alpha coronavirus)
  • NL63 (alpha coronavirus)
  • OC43 (beta coronavirus)
  • HKU1 (beta coronavirus)

Symptoms of common coronaviruses include cough, headache, sore throat, runny nose, fever, and general malaise. In persons with heart and lung disease, infants, older adults, and person with immune disorders, additional illnesses may include lower respiratory infections such as bronchitis and pneumonia.2

There are three human coronaviruses known to cause severe illness in humans.

The first coronavirus recognized as causing severe illness in humans was identified in 2003 and became known as Severe Acute Respiratory Syndrome (SARS). Health officials believe that the virus originated from an animal source, possibly a bat, and infected other animals prior to human transmission. The origin of this virus was traced to the Guangdong province of Southern China. Initial symptoms of SARS included headache, malaise, fever, muscle aches, shivering and diarrhea. Shortness of breath, cough, and diarrhea commonly occurred in the first or second week of illness and in serious cases, progressed rapidly to respiratory distress requiring intensive care.3 The outbreak was considered contained by July of 2003, and no cases of the illness have been reported since 2004. SARS was believed to have infected 8,096 individuals and resulted in 774 deaths.4

The second, Middle Eastern Respiratory Syndrome (MERS), was identified by health officials in Saudi Arabia in September 2012. The exact origin of the virus remains unknown; however, it is believed to have originated in bats and spread to camels prior to human transmission. Classic symptoms of MERS include cough, fever, and shortness of breath. Respiratory distress requiring intensive care and mechanical ventilation occurs in severe cases. While the fatality rate of MERS is estimated at 35 percent, health officials believe that the true fatality rate is lower since milder cases are likely not diagnosed. The virus is not easily transmitted, and most infections have occurred in health care settings among personnel providing care to infected individuals. While MERS has been reported in 27 countries, 80 percent of cases have been reported in Saudi Arabia.5 Only two cases of MERS have been reported in the U.S. and both involved health care providers residing and working in Saudi Arabia.6

The third and most recent is the novel SARS-Coronavirus-2 (SARS-CoV-2), which causes a collection of symptoms including severe illness that has become known as COVID-19. Initial reports began on January 8, 2020, when the CDC issued a health advisory alert regarding a cluster of pneumonia cases with links to a wholesale animal and fish market in Wuhan City, in the Hubei province of China. The initial health alert reported illness in 59 individuals with symptom onset dates beginning December 12, 2019 that included shortness of breath and fever. No deaths were reported and according to Chinese health officials, there were no reports of human to human transmission.7

Chinese health officials identified the virus as a novel coronavirus on December 31, 2019, and by the end of January 2020, 217 deaths among 9,776 confirmed cases had been reported. On January 30, 2020, the World Health Organization (WHO) declared the outbreak a “Public Health Emergency of International Concern” with health officials reporting that the origin of the virus was likely an unsanitary food market in Wuhan City, China. WHO officials suggested that infected individuals were exposed after consuming infected bats and snakes from the city’s market.8 One day later, the U.S. Department of Health and Human Services (HHS) Secretary Alex M. Azar II declared the novel coronavirus a U.S. public health emergency.9

COVID-19 Symptoms and Complications

Symptoms of COVID-19, the illness caused by SARS-CoV-2, include:10

  • Cough
  • Congestion
  • Runny nose
  • Shortness of breath
  • Difficulty breathing
  • Fever
  • Chills
  • Fatigue
  • Muscle aches
  • Body aches
  • Sore throat
  • Headache
  • New loss of taste or smell
  • Diarrhea
  • Nausea
  • Vomiting

Complications of the virus include pneumonia, acute respiratory failure, Acute, Respiratory Distress Syndrome (ARDS), acute kidney, liver, and heart injury, septic shock, disseminated intravascular coagulation (DIC), rhabdomyolysis (muscle breakdown), chronic fatigue syndrome, and blood clots.

Many complications may be caused by a condition known as a cytokine storm. This occurs when an infection triggers the immune system to flood the bloodstream with inflammatory proteins referred to as cytokines, which can damage organs and kill tissue.11 Health officials also believe that the virus may trigger a multisystem inflammatory syndrome in children and adolescents known as Multisystem Inflammatory Syndrome in Children (MIS-C). The CDC reports that they do not know what causes this condition but that many children who develop it have a personal health history of exposure to the SARS-CoV-2 virus or have been in contact with an infected individual.12

COVID-19 Broadly Defined to Include all SARS-CoV-2 Infections

According to the CDC’s August 5, 2020 interim case definition for Coronavirus Disease 2019 (COVID-19), a confirmed COVID-19 case is one where laboratory evidence indicates the presence of the SARS-CoV-2 virus by a molecular amplification test13 such as reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) or nucleic acid amplification test (NAAT).14

A probable COVID-19 case is a case where a person meets the clinical criteria for COVID-19 illness based on at least one symptom and the individual is also epidemiologically linked to another confirmed or probable case. The criteria for epidemiological linkage include close contact with a confirmed or probable case of COVID-19 disease or else being considered at risk based on criteria defined by public health officials during an outbreak. Probable cases are also cases confirmed by antigen testing, a rapid test considered less sensitive and not as reliable as molecular amplification tests.15 16

SARS-CoV-2 Variants

Multiple variants of the SARS-CoV-2 virus emerged in the fall of 2020 and continue to circulate worldwide. Like all viruses, SARS-CoV-2 continually evolve because genetic mutations happen during the genome’s replication. A variant is the result of one or more genetic mutations.17

The Centers for Disease Control and Prevention (CDC) classify SARS-CoV-2 variants into four distinct categories: Variant Being Monitored; Variant of Interest; Variant of Concern; and Variant of High Consequence. The variant’s transmissibility, the severity of illness, and the effectiveness of current medical treatments factor into the classification of each variant.

On May 31, 2021, the World Health Organization (WHO) announced the use of “simple, easy-to-say labels for SARS-CoV-2 Variants of Interest and Concern” and reported that letters of the Greek alphabet would be used to identify variants. While scientific names would continue to be used, WHO reported that:18

“While they have their advantages, these scientific names can be difficult to say and recall, and are prone to misreporting. As a result, people often resort to calling variants by the places where they are detected, which is stigmatizing and discriminatory. To avoid this and to simplify public communications, WHO encourages national authorities, media outlets and others to adopt these new labels.”

Monitored variants have included: Alpha (B.1.1.7), Beta (B.1.351), Delta (B.1.617), Gamma (P.1.), Epsilon (B.1.427 and B.1.429), Eta (B.1.525), Iota (B.1.526), Kappa (B.1.617.1), Mu (B.1.621, B.1.621.1), Zeta (P.2) and 1.617.3.

The Delta variant, which was designated a Variant of Concern by WHO in May of 2021 due to increased transmissibility. Public health officials noted that both vaccinated and COVID-19 recovered individuals could be susceptible to infection.19 By July 2021, the CDC acknowledged that both vaccinated and unvaccinated infected with the Delta variant were equally contagious.20

In early November 2021, the Omicron variant, which was initially identified in South Africa, was labeled a Variant of Concern by WHO due to the significant number of mutations.21 These mutations were associated with increased transmissibility and reinfection.

As of August 28, 2022, the Omicron variant is the predominant SARS-CoV-2 variant in the U.S. and remains a Variant of Concern.22 23

Public health experts admit that they are uncertain as to how effective the current authorized treatments and vaccines will be against novel SARS-CoV-2 variants.24 25

IMPORTANT NOTE: NVIC encourages you to become fully informed about covid-19 and the covid-19 vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.


1 Vandergriendt C. What Is a Coronavirus? Healthline Mar. 31, 2020.

2 U.S. Centers for Disease Control and Prevention. Common Human Coronaviruses. In: COVID-19. Feb. 13, 2020.

3 World Health Organization. SARS (Severe Acute Respiratory Syndrome). No date. (Accessed July 23, 2022).

4 U.S. Centers for Disease Control and Prevention. CDC SARS Response Timeline. In: About CDC 24-7. Apr. 26, 2013.

5 World Health Organization. Middle East respiratory syndrome coronavirus (MERS-CoV). In: Fact Sheets. Aug. 5, 2022.

6 U.S. Centers for Disease Control and Prevention. MERS in the U.S. In: Middle East Respiratory Syndrome (MERS). Aug. 2, 2019.

7 U.S. Centers for Disease Control and Prevention. Outbreak of Pneumonia of Unknown Etiology (PUE) in Wuhan, China. In: Emergency Preparedness and Response. Jan. 8, 2020.

8 Fisher BL. Coronavirus Vaccines on Fast Track as WHO Declares Global Public Health Emergency - NVIC Special Report: COVID-2019 Pandemic - Part 1. National Vaccine Information Center Feb. 5, 2020.

9 Global Biodefense Staff. Secretary Azar Declares Public Health Emergency for United States for 2019 Novel Coronavirus. Global BioDefense Jan. 31, 2020.

10 U.S. Centers for Disease Control and Prevention. Symptoms of COVID-19. In: COVID-19. Aug. 11, 2022.

11 WebMD. Complications Coronavirus Can Cause. Aug. 9, 2021.

12 U.S. Centers for Disease Control and Prevention. For Parents: Multisystem Inflammatory Syndrome in Children (MIS-C) associated with COVID-19. In: Multisystem Inflammatory Syndrome (MIS). Sept. 20, 2021.

13 U.S. Centers for Disease Control and Prevention. Coronavirus Disease 2019 (COVID-19) 2020 Interim Case Definition, Approved August 5, 2020. In: National Notifiable Diseases Surveillance System (NNDSS). Apr. 16, 2021.

14 U.S. Food and Drug Administration. Coronavirus Testing Basics. Feb. 28, 2022.

15 U.S. Centers for Disease Control and Prevention. Coronavirus Disease 2019 (COVID-19) 2020 Interim Case Definition, Approved August 5, 2020. In: National Notifiable Diseases Surveillance System (NNDSS). Apr. 16, 2021.

16 U.S. Centers for Disease Control and Prevention. Guidance for Antigen Testing for SARS-CoV-2 for Healthcare Providers Testing Individuals in the Community. In: COVID-19. Apr. 4, 2022.

17 U.S. Centers for Disease Control and Prevention. Science Brief: Emerging SARS-CoV-2 Variants. In: COVID-19. Jan. 28, 2021.

18 World Health Organization. WHO announces simple, easy-to-say labels for SARS-CoV-2 Variants of Interest and Concern. May 31, 2021.

19 Dillon N. Highly contagious COVID B.1.617 variant first identified in India re-classified as ‘global concern,’ WHO says. New York Daily News May 10, 2021.

20 U.S. Centers for Disease Control and Prevention. Statement from CDC Director Rochelle P. Walensky, MD, MPH on Today’s MMWR. In: CDC Newsroom. July 30, 2022.

21 World Health Organization. Classification of Omicron (B.1.1.529): SARS-CoV-2 Variant of Concern. Nov. 26, 2021.

22 U.S. Centers for Disease Control and Prevention. First Confirmed Case of Omicron Variant Detected in the United States. In: CDC Newsroom. Dec. 1, 2021.

23 U.S. Centers for Disease Control and Prevention. Variant Proportions. In: COVID Data Tracker. Aug. 27, 2022.

24 Mascola JR, Graham BS, Fauci AS. SARS-CoV-2 Viral Variants—Tackling a Moving Target. JAMA  February 11, 2021.

25 U.S. Centers for Disease Control and Prevention. What You Need to Know about Variants. In: COVID-19. Aug. 11, 2022.

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