2. Could a longer duration of NA therapy enhance the success of off-treatment durability? For many available therapy cessation studies, the mean NA therapy duration was approximately 1.5-3 years. There is emerging evidence demonstrating intrahepatic covalently closed circular DNA (cccDNA) could actually decrease profoundly after more than 5 years of NA therapy ; a low intrahepatic HBV cccDNA level could be the key to successful off-treatment durability.