SARS-CoV-1 was more aggressive and lethal than SARS-CoV-2. However, SARS-CoV-2 spreads faster, sometimes with hidden symptoms, allowing each infected person to infect several others. The current estimate is about three, but we scientists won’t know the real number until we can test a lot more people, and can understand the role of people without symptoms.
The most important difference is that contact tracing – or finding out who was exposed to someone infected with the virus – was relatively easy: Everyone had severe symptoms in two to three days.
With SARS-CoV-2, it takes about two weeks for symptoms to appear, and many people don’t have any symptoms at all. Imagine asking someone whom they had contact with for the last two weeks! You can accurately remember most people you had contact with for the past two days, but two weeks? This critical tool for pandemic control is very challenging to implement. This means that the only safe thing to do is to maintain quarantine of everyone until the pandemic is under control.
— Marilyn Roossinck, environmental microbiologist at Pennsylvania State University, writing in The Conversation