I just started my second pack sprintec. how effective is it without a condom?

Very effective: Sprintec is a combined estrogen and progestin oral contraceptive pill. If it is taken exactly as precribed the chance of unintended pregnancy is less than 1%. It sounds like you have appropriately used back-up condoms for the first cycle. Condoms need not be used for contraceptive purposes as you continue the Sprintec, but are still needed to prevent STD's/STI's.