COVID-19 vs SARS and MERS

SARS, MERS and COVID-19 have become household names for many of us during this pandemic, but what do we really know about them? Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS) and Coronavirus Disease 2019 (COVID-19) all originate from coronaviruses, a specific type of virus that features spiky proteins surrounding the surface of the virus. But they're not the same, obviously, so what gives?

What Do COVID-19, SARS, and MERS Have In Common?

While there are literally hundreds of coronaviruses, only seven have managed to jump to humans so far. The last of which was the SARS-COV-2, or the novel coronavirus that causes COVID-19. Of the seven that have made the jump to humans, four cause mild respiratory infections, like the common cold. But the latest three, SARS, MERS, and COVID-19, are more likely to cause serious, potentially fatal illnesses.

These illnesses have a lot in common:

• Fever — A fever of greater than 100.5 degrees Fahrenheit (38 degrees Celsius) is the single most prevalent symptom for all three diseases.
• Shortness of breath — All three of these illnesses can cause shortness of breath.
• Cough — While COVID-19 is marked by a dry cough, all three are known to be associated with coughing.
• Method of transmission — All of these viruses are spread via respiratory droplets spread through coughing or sneezing, as well as contact with contaminated objects or surfaces.
• Progression — In all three diseases, these symptoms can progress to pneumonia and respiratory failure, which may require oxygen or ventilation. Kidney failure, as a result of respiratory failure, has also been reported with all three illnesses. COVID-19, SARS and MERS symptoms may worsen later in the illness.
• Risk — Those with chronic disease, lung conditions, diabetes, compromised immune systems, or who are older are more at risk of complications from all of these diseases.
• No vaccines or treatment — To date, there is no vaccine or treatment for any of the three viruses.

What makes SARS, MERS, and COVID-19 different? Well, they're different in some key ways. Namely:

Incubation Period of COVID-19, SARS and MERS

The incubation period, which is the time from exposure until the first symptoms begin, varies slightly between the three illnesses. All three viruses officially have an incubation period of 2-14 days. But the average incubation period for MERS and COVID-19 is 5 days, while the average incubation period for SARS is 6.37 days.

Transmissibility and Degree of Contagion in COVID-19 vs SARS and MERS

In addition to the average incubation period, researchers consider something called the serial interval to evaluate transmissibility and degree of contagion. In a chain of infection from one person to the next, the serial interval is the time between the start of symptoms in the primary patient (the infector) and onset of symptoms in the patient receiving that infection (the infectee).

While SARS is considered extremely contagious, it has an average serial interval of 8.4 days compared with MERS, which has an average serial interval of 14.6 days or COVID-19, which has an average serial interval of only 3.96 days. This became another clue for researchers that the virus might actually be transmitted by individuals who were presymptomatic or asymptomatic. In other words, they could be actively infected and shedding virus even before beginning to show symptoms.

This feature had not been seen before with SARS or MERS, and it has made COVID-19 much more difficult to contain or even mitigate. So even though SARS was considered more contagious by the classical definition, COVID-19 has been a more difficult public health challenge, specifically because of asymptomatic and presymptomatic transmissions.

Measuring the Contagion Levels of COVID-19, SARS, and MERS

Another measure of contagion is R0 (called “R naught”). It represents the viral reproduction number and is based on the average of how many people an infected person will also infect during their contagion period. Using R0 as a measure for contagion is most important for new diseases when no immunity to the disease exists in the general population and no countermeasures like vaccines or cures exist.

The larger the R0 number, the more infectious the disease. Numbers less than 1 generally indicate diseases that can be easily contained and will die out. Numbers equal to 1 indicate diseases that may persist, but that could be eradicated eventually. Numbers greater than 1 indicate diseases that have the potential to create epidemics or pandemics.

Based on infection rates and testing rates, Italy arguably has the largest body of comprehensive data available for COVID-19. The average calculated R0 for Italy for COVID-19 is 2.43-3.10. The R0 for the 2002-2004 SARS outbreak was calculated to be 2-4. By comparison, the R0 for the 2012 emergence of MERS was less than 1.

Death Toll and Mortality Rate

COVID-19 has undoubtedly led to a higher death toll. As of the end of the day Friday, April 24, at midnight GMT (8 pm Eastern Time), COVID-19 had infected a reported 2,828,826 cases worldwide with a reported death toll of 105,825. SARS cases were reported as 8098 infections and 774 deaths. MERS cases were reported as 2521 infections and 866 deaths. Despite resulting in a higher number of deaths, the mortality rate for COVID-19 is actually lower than both SARS and MERS. According to the WHO, COVID-19’s mortality rate was 3.4%, as of March 3. The estimated mortality rate for SARS was 10%, while MERS had a global death rate of 34.3%. Since these viruses were easier to contain, however, we didn’t see the high death tolls COVID-19 has caused because ultimately it doesn't matter if a virus only kills 3% if it can infect everyone on the planet in the course of a short time.

Researchers have learned a lot about emerging pathogens by studying these three coronaviruses’ similarities and differences. We’ve all learned the importance of hand hygiene, which is incredibly important to minimize the transmission of all these diseases and the importance of social isolation to slow outbreaks when vaccines and viable treatments aren’t available. Everything we learn might help up not only with this outbreak but with the next.

Copyright 2020, Wellness.com