Introduction: Possibility of breakthrough infection to Covid-19 variants which may cross vaccine induced immunityas immunity acquired from natural COVID-19 infection or vaccines is not absolute and reinfections postnatural COVID-19 infections, as well as vaccine breakthrough infections, are not uncommon. Furthermore, lack of data is available on breakthrough infection as well as reinfection in India especially in Bihar. Thus, the present study is undertaken to find out magnitude of breakthrough infection and re-infection of COVID 19 and to find out factors associated with breakthrough infection and re-infection