Reply #11: you are contgagious from the time you show any symptoms...

[northernlights]

even mild symptoms. That's not the incubation period. You are infected with the flu. By not stopping, resting, staying at home to avoid contact with others, and caring for yourself, the infection (eg virus) spreads.

The incubation period lasts from the time of exposure to the time that the virus is replicating within your cells. You are infected from the time the virus is replicating -- that is the definition of infected. Your symptoms start after your immune system has picked up on the virus -- and there needs to be enough virions circulating for that to happen -- and starts fighting the infection. Initial symptoms are mostly a result of the immune system actions in response to the virus, not the virus itself. If you don't take care of yourself, the infection will progress, spread to more cells, reproduce more virions.

I've avoided getting serious colds or flus for decades simply by taking a few days off and nurturing myself at the onset of symptoms, so my body can fight off the infection while viral levels are still relatively low. Not toughing it out until I'm obvious sick.