question

i used to get full blown flu or cold without having an outbreak at the same time and OB at different times. in the last year, i am having outbreaks without having the symptoms of the flu or cold.
does anyone know what causes the flu or cold without an outbreak and what causes the OB with very mild or even without any flu or cold symptoms?
how does the body chooses to go into proper flu mode or into OB?

thank you