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Abstract : The recent rapid worldwide spread of SARS-CoV-2 has established a pandemic of potentially serious disease in the highly susceptible human population. Key issues are whether humans have pre-existing immune memory that provides some protection against SARS-CoV-2 and whether SARS-CoV-2 infection generates lasting immune protection against reinfection. The adage that ‘natural infection gives better immunity than vaccination’ have been held as a long-standing belief, including among health professionals. As for SARS-CoV-2, the superiority of vaccine-based immunity has been proven in immunogenicity studies of frontier vaccine candidates: post-vaccination antibody assays showed higher neutralizing anti-S-IgG compared to that of convalescent plasma. The first case, a 34-years-old woman, confirmed COVID-19 for the 2nd times, asymptomatic; RT PCR result confirmed SARSCoV-2 and the spike RBD result was positive (1786 U/mL). The second case was a 35-years- old woman with cough, rhinorrhoea, sore of the throat for a weekand history of fever a week ago. This is the 2nd times she got COVID-19.RT PCR result confirmed SARSCoV-2 and spike RBD result was positive (15.940 U/mL). The third case was a 39-years-old woman with diagnosed COVID-19 for the 2nd times. She came with common cold, headache and previously had history of fever for 2 days. RT PCR confirmed SARSCoV-2 and the spike RBD result was positive (3538 U/mL). All of them are health care worker in a hospital and had been got vaccine for Sinovac 2 dose and Moderna as a booster. COVID‐19 reinfection does not carry a higher risk of severe disease. The mechanism of reinfection is not clear. Viral evolution might favour reinfections and spike mutations, particularly in the receptor binding domain (RBD) in coronavirus infection. Further studies are required especially with the continuously newly emerging variants with the unpredictable risk of reinfection.