>>11531400Two factors:
1) the virus has to infect your cells, and to do this it has to overhelm your natural defences and successfully replicate (which isn't a given, since viruses are naturally unstable, both a blessing and a curse)
2) Unless it is a chronic virus capable of eluding your adaptive defenses, the virus is on a timetable. Once you mount your adaptative response, it is done for.
Therefore, the higher the viral load, the higher the chances to successfully infect the host, and the higher the payoff from the infection.
