How does SARS-CoV-2 Compare to SARS-CoV?

Severe acute respiratory syndrome coronavirus (SARS-CoV) is a viral infection caused by a coronavirus that results in a flu-like respiratory illness. There was an outbreak of SARS-CoV in 2002 that led to a pandemic in 2003, but the virus was quickly contained.

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SARS-CoV-2 is a novel coronavirus first identified in Wuhan, China, in December 2019. It has since become a pandemic throughout 2020. Infection with SARS-CoV-2 leads to a severe respiratory illness called COVID-19.

What is Coronavirus?

A coronavirus is a common virus from a large family of viruses that can cause illnesses such as the common cold and SARS. Not all coronaviruses are dangerous, but some can be fatal.

Coronaviruses can be spread in a mutated form from animals to humans. The 2002 SARS-CoV pandemic first passed from civet cats to humans. The exact origin of SARS-CoV-2 has not yet been identified during the 2020 pandemic.

How is Transmissibility Measured?

The basic reproductive rate for an infectious disease is called R₀. R₀ shows the average or expected number of people that can be infected by one infectious person.

It is calculated by taking the number of potential people to be infected, the length a person is infected for, which can increase viral transmissibility, and the transmissibility of the disease based on the nature of the disease itself and parameters in the population, such as age and nutrition.

The longer a person is infected with a transmissible disease, the more likely R₀ for that person will increase. If R₀ is above one, disease transmission can be expected to increase exponentially in a population and result in a pandemic.

Certain diseases are not as easily transmissible as others; some require direct contact with body fluids (as in HIV), and others are transmissible through particles in the air, as is the case with SARS-CoV and SARS-CoV-2. Airborne particles are much easier to spread than direct contact with the skin or body fluids.

R₀ can be reduced through vaccination, quarantine, physical and social distancing, or increasing sanitary measures such as using hand sanitizers and handwashes.

What is SARS-CoV?

SARS-CoV is a viral respiratory illness that was first reported in China in 2002 and identified in February 2003. It caused an outbreak of severe acute respiratory syndrome (SARS) that led to a pandemic across North America, South America, Europe, and Asia.

SARS-CoV did pose a high fatality risk, but the pandemic lasted a short period, ending in June 2003. There were 8,098 cases reported globally, and 774 deaths, with a case fatality rate of 9.7 percent.

SARS-CoV was believed to have been initially transmitted from small mammals in a mutated form to humans.

Symptoms

Symptoms of a SARS-CoV infection are:

• Fever
• Fatigue
• Muscle pain
• Headache
• Loss of appetite
• Diarrhea
• Shivering

In the later stages of the infection, a person can experience a dry cough, breathing difficulties, and low levels of oxygen in the blood, which can be fatal.

Transmission and R₀

SARS-CoV is an airborne virus and is spread through small droplets of saliva that are released into the air through coughs and sneezes. When another person breathes in these droplets, an infection can occur.

SARS-CoV can also be transmitted via fomites (an object or surface infected with the virus) such as door handles. The virus can also be transmitted through feces if a person does not wash their hands after going to the toilet.

SARS-CoV was a nosocomial infection, meaning it was mainly transmitted in healthcare facilities. Transmission mainly occurred during the second week of infection.

At the beginning of the outbreak in 2002, the R₀ value was estimated to be between 2·0 and 3·0 but was reduced to 1·1.

A 2020 study comparing SARS-CoV and SARS-CoV-2 stated that the viral load is higher and lasts longer in the lower respiratory tract in people that experience severe COVID-19 illness. In SARS-CoV, upper respiratory tract infections did not occur with lower respiratory tract infections, meaning the transmission of SARS-CoV was lower than SARS-CoV-2 in the first 5 days of infection.

A comparison of the transmissibility and severity of illness caused by the two viruses is below.

	SARS-CoV	SARS-CoV-2
Transmissibility R0	2·4	2·5
Incubation period	2 to 7 days	4 to 12 days
Days between symptom onset and maximum level of infectivity	5 to 7 days	0 days
Amount of patients with mild illness	Low	High
Amount of patients needing hospitalization	Most patients (over 70 percent)	Few patients (20 percent)
Amount of patients needing intensive care	Most patients (40 percent)	1 in 16,000
Risk factors for severe illness	Increased age, underlying illnesses	Increased age, underlying illnesses

Treatment

There is no vaccine for SARS-CoV and any treatment is supportive. This means the body is supported while it fights the virus naturally, with ventilators to assist breathing, antibiotics to kill bacteria that cause pneumonia, or steroids to reduce inflammation in the lungs.

What is SARS-CoV-2?

SARS-CoV-2 is genetically similar to SARS-CoV.

The outbreak began in December 2019, and by June 20, 2020, the global case rate has reached 14,348,858. 603,691 deaths by June 20, 2020, have also occurred. The initial global spread was heightened through infection on a cruise ship in Japan, a religious mass gathering in South Korea, and in skiing resorts in Italy and Austria. As a result, epidemics occurred in many countries.

Symptoms

SARS-CoV-2 causes mild symptoms in most cases, and can many people are asymptomatic. The possible symptoms of a SARS-CoV-2 infection are:

• High temperature
• A continuous, dry cough
• Loss of the sense of taste and smell.

SARS-CoV-2 is less likely to be fatal than SARS-CoV. However, SARS-CoV-2 is more easily spread.

Transmission and R₀

SARS-CoV-2 has an approximate R0 value of 2·5. For R0 to reach less than 1, the transmission rate would need to be reduced by over 60 percent.

SARS-CoV-2 can be spread through droplets released by coughing and sneezing that are then breathed in by another person.

When comparing the aerosol and surface transmissibility of SARS-CoV and SARS-CoV-2, researchers found that SARS-CoV-2 was detected for up to 72 hours after it was applied to plastic, stainless steel, copper, and cardboard. The differences in the viability of these two viruses found in this study, and the reduction in the amount of infectious virus on each surface, are detailed below.

Environment	SARS-CoV	SARS-CoV-2
Aerosol	Viable for 3 hour experiment time Infectious titer reduced from 104.3 to 103.5 TCID50 per milliliter.	Viable for 3 hour experiment time Infectious titer reduced from 105 to 102.7 TCID50 per liter of air
Cardboard	No viable virus found after 8 hours	Viable virus found after 72 hours
Copper	No viable virus found after 8 hours	No viable virus found after 4 hours
Plastic	Viable for 6.8 hours	Viable for 6.8 hours
Stainless steel	Viable for 5.6 hours Infectious titer reduced from 103.7 to 100.6 TCID50 per milliliter after 72 hours	Viable for 5.6 hours Infectious titer reduced from 103.7 to 100.6 TCID50 per milliliter after 48 hours

This study suggests that the stability of the two viruses on surfaces and aerosols is similar. It also suggests that differences in the transmissibility of these viruses may result from other factors such as higher viral loads in the upper respiratory tract in SARS-CoV-2 than in SARS-CoV.

Studies have suggested that SARS-CoV was less able to survive in warmer temperatures, with its infectious titer reducing at 38C and 95% humidity. At 4C, SARS-CoV was able to survive for 28 days. There is currently no definitive data on the effect of temperature on SARS-CoV-2, but the insight into SARS-CoV suggests it may be less able to survive in warmer temperatures.

Treatment

There is no vaccine for SARS-CoV-2 and any treatment is supportive. This means the body is supported while it fights the virus naturally, with ventilators to assist breathing and maintain good oxygen levels in the blood.

Summary

While SARS-CoV is no longer a pandemic threat, SARS-CoV-2 is a current and evolving pandemic. SARS-CoV-2 has a high amount of people with mild or no symptoms, meaning that detecting and tracking the transmission and then controlling the virus is harder than with SARS-CoV.

Those most at risk of severe illness from SARS-CoV and SARS-CoV-2 are older people and those with underlying health conditions. Treatments are similar for both SARS-CoV and SARS-CoV-2, with neither disease having an effective vaccine. As such, all treatments are supportive.

Further Reading

• All Coronavirus Disease COVID-19 Content
• What Mutations of SARS-CoV-2 are Causing Concern?
• What is the Clinical Impact of COVID-19 on Cancer Patients?
• Can Pets Get COVID-19?
• An Overview of the SARS-CoV-2 Vaccines

Written by

Lois Zoppi

Lois is a freelance copywriter based in the UK. She graduated from the University of Sussex with a BA in Media Practice, having specialized in screenwriting. She maintains a focus on anxiety disorders and depression and aims to explore other areas of mental health including dissociative disorders such as maladaptive daydreaming.