Why does COVID-19 appear more infectious than SARS?
The COVID-19 R0 factor is 2-3, while SARS had an R0 factor of 2-5. However, COVID-19 has infected around 130,000 people and growing, while SARS totalled just under 9000 people infected.
Why is COVID-19 spreading faster and wider than SARS? What other factors have let COVID-19 reach pandemic levels, while SARS was contained and eradicated? Could the R0 factor be higher than believed? Was it initially slower to be contained?
Full disclosure, I'm not in medicine or a medical scientist. I'm a software developer and data scientist, and this has peaked my interested in the spread of infectious disease.
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It is possible that with SARS fewer people were transmitting the virus, but those who were were "super-spreaders". R_0 is an average of those transmitting.
Source:
www.cidrap.umn.edu/news-perspective/2020/01/data-suggest-ncov-more-infectious-1918-flu-what-does-mean
Another possibility is that the high mortality rate in SARS actually prevented it from spreading widely.
Source:
nautil.us/issue/83/intelligence/the-man-who-saw-the-pandemic-coming
The reason that covid-19 is more infectious than SARS is likely to have mild symptoms in healthy people. That's why there are significant difficulties in discerning infected people, and infected people are active and spread a lot. I guess this is why covid-19 is more infectious than SARS. Even among experts, the evaluation of covid-19's infection power is constantly changing. So the exact answer to the questioner does not currently exist.
The viruses are acting differently. SARS-CoV-2 virus is much more infectious with a much higher viral replication rate, and with people exhaling the virus in the pre-symptomatic phase whereas SARS this was not happening. Once the infected individual becomes symptomatic their bodies are producing antibodies which helps shut down viral particle shedding though virus is still being transmitted by cough which aerolizes the virus at a further distance then just by exhalation.
The nine patients, who were admitted to the same Munich hospital, were studied because they had had close contact with an index case. Cell cultures and real-time polymerase chain reaction (RT-PCR) were done on throat swabs and samples of sputum, stool, blood, and urine. Throat swabs showed very high viral shedding during the first week of symptoms.
The findings contrasted starkly with those from the 2003 outbreak of SARS in terms of viral load. "In SARS, it took 7 to 10 days after onset until peak RNA concentrations (of up to 5x105 copies per swab) were reached," the researchers wrote. "In the present study, peak concentrations were reached before day 5, and were more than 1,000 times higher."
but the mean incubation period is 5 days. www.cidrap.umn.edu/news-perspective/2020/03/study-highlights-ease-spread-covid-19-viruses
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