After you are infected, your immune system:
1. Has to notice that something is up
2. Has to work out which antibodies are effective at stopping it
3. Has to mass produce those antibodies to eliminate the infection
4. Stops when it stops getting signals that the virus is still active
Before step 3, from the point when you are infected until your immune system has started acting at full power, you are infecting other people and don’t yet have any symptoms. That’s what people usually call the incubation period. It’s only after your immune response has ramped up that you start feeling the effects.
During the incubation period there isn’t enough virus in your system for your brain to be alerted to the problem. During that time, the virus is replicating while it’s slipping under your body’s radar. Once enough of the virus exists in your system, your body will alert your brain to the “invasion” and your brain will direct your immune system to mount a defense. Until then, your brain doesn’t realize it’s there.
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