History repeating itself? SARS VS COVID-19
A molecular comparison of the SARS and COVID-19 pathogens
There is an 80% genomic similarity between SARS-CoV that caused the SARS epidemic and SARS-CoV-2 that is causing COVID-19. They use the same receptor, called ACE2, on the human cell, to enter and infect it. For two RNA viruses, 80% is very significant similarity, so why are the outbreaks turning out so differently if the viruses are so closely related?
Although we’re living through the first pandemic caused by a coronavirus, it is not the first time they have caused global chaos. The words SARS and MERS may also be familiar to many of us.
Symptoms most of us can now recite off head, high fever, headache, body aches and a dry persistent cough.. also define SARS that broke out in Guangzhou, China in 2002. How similar are these outbreaks in their severity, in their genetic makeup and how the world has responded?
The case and death count will reveal an almost gigantuan difference between the two coronavirus outbreaks. Worldwide there were around 8000 cases of SARS and almost 800 deaths. The disease reached 27 countries. The outbreak was completely contained within two years.
SARS-CoV-2 which causes COVID-19, is of course an ongoing pandemic, to date there have been over 80 million documented cases and tragically, 1.7 million deaths.
Staring at the numbers it seems impossible to compare the two, and weirdly, if we look at the severity of disease, SARS actually appears more deadly. While more than 70% of SARS patients required hospitalisation, only around 20% of COVID-19 patients end up in hospital for treatment.
So what are the differences that have made COVID-19 so much more devastating?
SARS and SARS-CoV-2 have surprisingly similar transmission rates, what we have often heard termed as the ‘R rate’, SARS being approximately 2.3 and SARS-CoV-2 being 2.4.
The R rate is of course volatile and as we have been reminded often on the news, can be brought down and controlled, but they are roughly similar for both viruses.
The SARS-CoV-2 pathogen however has a significantly long incubation period, that is, how long can the virus remain in the body before you potentially become symptomatic. Its incubation period can be up to 12 days whereas SARS was only up to 5.
Another big difference between the two viruses is at which point is your viral load the highest and consequently, when are you the most contagious?
Studies showed that during the SARS epidemic, patients were most contagious between days 6-11. That allows crucial time for carriers to become aware that they need to isolate. COVID-19 patients are typically most contagious much earlier after infection.
So what about the global response? Were we just faster in 2002? Did we catch it early?
The first case of SARS was recorded in mid-November in China. It wasn’t until February 11th that the health officials in the Guangdong province began to hold conferences on the disease to inform the local community. Everyone was advised to practice good hand hygiene and ventilate their homes.
The Chinese government shared very little information with the World Health Organisation (WHO) until April. There were many disruptions to the flow of information from China which would take too long to list… point is, we were not fast with the response.
There were about 5 months between the first case and any serious action being taken by WHO. This time round the first SARS-CoV-2 case is suspected to have been in December 2019. WHO declared the pandemic the following March which is actually significantly faster than in 2003.
Whilst SARS was contained by 2004 with no vaccine ever developed, it looks like a vaccine is our only exit from the COVID-19 pandemic.
It seems to me the huge noticeable difference is that COVID-10 patients are largely asymptotic or show symptoms in a much more delayed time frame. The vast majority of SARS patents were severely symptomatic within the first 3 days of exposure.
The truth is tracking the spread of a virus and implementing the necessary quarantines are much easier when the symptoms are more immediately visible and aggressive.
We are yet, I am sure to uncover so many secrets behind this mystery and as more information reveals itself we will have more answers.
With the information now available to us, I would argue the most COVID-19 is that much more devestating because of how it hides in unaware asymptomatic patients, the longer you are naive to the fact you may be contagious, the more people you potentially expose.
References
THE SARS EPIDEMIC AND ITS AFTERMATH IN CHINA: A POLITICAL PERSPECTIVE https://www.ncbi.nlm.nih.gov/books/NBK92479/
Here’s How COVID-19 Compares to Past Outbreaks https://www.healthline.com/health-news/how-deadly-is-the-coronavirus-compared-to-past-outbreaks#1918-influenza
Can we contain the COVID-19 outbreak with the same measures as for SARS? https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30129-8/fulltext
The mysterious disappearance of the first SARS virus, and why we need a vaccine for the current one but didn’t for the other https://theconversation.com/the-mysterious-disappearance-of-the-first-sars-virus-and-why-we-need-a-vaccine-for-the-current-one-but-didnt-for-the-other-137583
SARS: how a global epidemic was stopped https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2636331/
COVID-19 situation update worldwide, as of week 52 2020 https://www.ecdc.europa.eu/en/geographical-distribution-2019-ncov-cases
Comparing SARS-CoV-2 with SARS-CoV and influenza pandemics https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30484-9/fulltext