Can you relapse after recovering from the virus?
That doesn’t happen with these respiratory viruses. The symptoms that drag on are your body’s response to the virus, but the virus is gone after a few days. I take great umbrage at the lengths of time you are meant to be infectious for because it is just not true. Nine days is nonsense. You don’t excrete a live virus that long.
Those studies are not checking for live virus, they are checking for genome. They do something called a PCR test (polymerase chain reaction), which is the test we are using to diagnose patients. It doesn’t tell you that you have live virus in your nose, it tells you have had it. For about 72 hours of a viral infection you have a live virus. In children it can last for longer – four or five days have been observed in flu.
So, there’s a big difference between how long we can detect the virus and how long they can infect someone else. With this coronavirus the only way you can say, yes, they are still shedding live virus - which is the only thing that will infect someone else, is if you take that sample from the patient and extract it and put it on tissue culture cells and then see it growing. That is done very rarely. There are not a lot of studies that look at live viruses. It is very easy to do PCR tests. It is harder to do live virus studies.
How long are people contagious before symptoms appear?
The likelihood is up to 48 hours before. The symptoms are your body’s response to the virus. This is what is called an acute virus, so its way of dodging your immune system is to get into the upper respiratory tract and get through the epithelial cells into your system and replicate like mad.
The way these viruses have evolved and the way your body responds is an acute inflammatory reaction, so lots of histamine and something called cytokines are produced that ramp up your immune response. One of the first things to appear is that temperature, because the virus is affecting a big area - your whole upper respiratory tract. You get a big cytokine response, your temperature shoots up and you feel horrible.
With this
novel virus you get a dry cough form. That initial irritation and the cough is what the virus has evolved to produce. That cough is what sends the virus onto its next host. What we think of as the cold or the cough is actually your body’s response to the infection in the cells. These symptoms last much longer than the virus is live.
For whatever reason, the common colds, which are also a type of coronavirus, don’t cause this same response.
Influenza always does. Influenza also causes pandemics because something about that virus causes a larger immune response.