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


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.17

In the United Kingdom, the B.1.1.7 variant emerged in September 2020, and as of January 22, 2021, it was determined to be the dominant circulating strain in England. The transmissibility of this variant is reportedly greater than other circulating SARS-CoV-2 virus variants.18 As of April 10, 2021, the B.1.1.7 had been reported by 52 U.S. jurisdictions, and cases continue to increase.19 20 21 Health officials report that this variant appears to be 30 to 80 percent more transmissible and increased a person’s risk of death by 30 percent.22 23

The B.1.351 variant was initially detected in Nelson Mandela Bay in South Africa in early October, 2020. By December 2020, this variant was found to be the predominant variant circulating in Zambia. It is not currently reported to be associated with an increase in disease severity.24 This variant was initially detected in New York in November 2020 and now accounts for approximately 25 percent of all specimens collected. Health officials report that the current COVID-19 vaccines may not be effective against this strain.25 As of April 10, 2021, this variant had been reported by 36 U.S jurisdictions.26

The P.1. variant was first detected in Japan in four travelers from Brazil. In late December 2020, 42 percent of positive samples collected in Manaus, the largest city in the Amazon region of Brazil, were the P.1. variant. Public health officials have expressed concerns that this variant may be transmitted more effectively or be responsible for re-infection.27 As of April 10, 2021, 31 U.S jurisdictions had reported the presence of the variant.28

On February 11, 2021, the Journal of the American Medical Association (JAMA) published a letter from researchers reporting on the novel SARS-CoV-2 variant  CAL.20C, that had emerged in late 2020 in Southern California. By mid-January 2021, this variant was found to account for 35 percent of SARS-CoV-2 specimens from California, and 44 percent of specimens from Southern California. The infectiousness of this strain or its impact on disease severity was reported as unknown.29

Health experts admit that they are uncertain as to how effective the current authorized treatments and vaccines will be against these novel variants.30

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.

« Return to Vaccines & Diseases Table of Contents

Updated Apr. 26, 2021


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

2 U.S. Centers for Disease Control and Prevention. Common Human Coronaviruses. Feb. 13, 2020.

3 WHO. SARS (Severe Acute Respiratory Syndrome). No date.

4 U.S. Centers for Disease Control and Prevention. CDC SARS Response Timeline. Apr. 26, 2013.

5 WHO. Middle East respiratory syndrome coronavirus (MERS-CoV). Mar. 11, 2019.

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

7 U.S. Centers for Disease Control and Prevention. Outbreak of Pneumonia of Unknown Etiology (PUE) in Wuhan, China. Health Alert Network 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 DHHS. Secretary Azar Declares Public Health Emergency for United States for 2019 Novel Coronavirus. Press Release Jan. 31, 2020.

10 U.S. Centers for Disease Control and Prevention. COVID-19  Symptoms of Coronavirus. Feb. 22, 2021.

11 WebMD. Complications Coronavirus Can Cause Aug. 19, 2020.

12 U.S. Centers for Disease Control and Prevention. Multisystem Inflammatory Syndrome in Children (MIS-C). Feb. 25, 2021.

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

14 U.S. Food and Drug Administration. Coronavirus Testing Basics. Nov. 6, 2020.

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

16 U.S. Centers for Disease Control and Prevention. COVID-19 Interim Guidance for Antigen Testing for SARS-CoV-2. Dec. 16, 2020.

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

Emergence of SARS-CoV-2 B.1.1.7 Lineage — United States, December 29, 2020–January 12, 2021. MMWR Jan. 22, 2021; 70(3):95–99.

19 Galloway SE, Paul P, MacCannell DR, et al. Emergence of SARS-CoV-2 B.1.1.7 Lineage — United States, December 29, 2020–January 12, 2021. MMWR Jan. 22, 2021: 70(3);95–99.

20 U.S. Centers for Disease Control and Prevention. US COVID-19 Cases Caused by Variants. Apr. 10, 2021.

21 U.S. Centers for Disease Control and Prevention. Variant Proportions. In: COVID Data Tracker. Apr. 20, 2021.

22 Mallapaty S. What’s the risk of dying from a fast-spreading COVID-19 variant? Nature Feb. 5, 2021.

23 Mascola JR, Graham BS, Fauci AS. SARS-CoV-2 Viral Variants—Tackling a Moving Target. JAMA. Published online February 11, 2021. doi:10.1001/jama.2021.2088.

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

25 Rettner, R. New coronavirus variant in NYC has vaccine-evading mutation. LiveScience Feb. 25, 2021.

26 U.S. Centers for Disease Control and Prevention. US COVID-19 Cases Caused by Variants. In: COVID-19. Apr. 10, 2021.

27 Kupferschmidt K. New coronavirus variants could cause more reinfections, require updated vaccines. Science Jan. 15, 2021

28 U.S. Centers for Disease Control and Prevention. US COVID-19 Cases Caused by Variants. In: COVID-19. Apr. 10, 2021.

29 Zhang W, Davis BD et al. Emergence of a Novel SARS-CoV-2 Variant in Southern California. JAMA  February 11, 2021.

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

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