China went into a lockdown that no western nation is capable of. It has been shown in several places now that lockdowns absolutely slow and can eventually stop new cases. It has also been shown that to go about our normal lives means that cases double every two to three days. Until you've gotten this you are completely susceptible to infection. You have no immunity to it at all. There is nothing your body can do to prevent the infection. You will get infected if exposed. Then it's just a roll of the dice how serious your case is.