Why are people getting reinfected despite taking 2 doses of Covid vaccine?

Why are people getting reinfected despite taking 2 doses of Covid vaccine?

37 doctors of Sir Ganga Ram Hospital have tested Coronavirus positive. Out of them, 32 doctors are in home isolation while 5 are hospitalized for treatment. Many doctors have administered both doses of the Covid-19 vaccine during the vaccination campaign that began on January 16. In view of the increasing cases of Coronavirus in Delhi, the state government has implemented a seven-hour night curfew till April 30.