Our findings were similar to those from central Taiwan in a younger aged cohort of 12-15 years (97.3%).10 Loss of HB vaccine immune memory could be easily detected by low anti-HBs (<10 mIU/mL) production following one dose of booster HB vaccination. Defining the presence of HB vaccine HSP activation immune memory could be problematic because production of higher anti-HBs (>10 mIU/mL) 1 month after booster vaccination may result from primary immune response or anamnestic response. Most studies gave a booster dose of the vaccine

to seronegative (anti-HBs <10 mIU/mL) subjects who had completed the HB vaccination in infancy. Blood samples were taken before and 3-4 weeks after vaccination. If the postvaccination serum remained seronegative, this subject was considered to have lost immune memory to HB vaccine antigens. However, there was a group of subjects who mounted low-level anti-HBs (10-100 mIU/mL) responses after one dose of the HB vaccine. The interpretation for these subjects was less

clear. They might manifest an anamnestic response or have lost immune memory and mounted a primary response. This study aimed to clarify this issue by studying early responses to HB vaccines. Our results demonstrated that early responders (anti-HBs ≥10 mIU/mL at 7-10 days after vaccination; groups B and C) eventually developed a significantly higher anti-HBs GMT at 1 month and 6 months compared with the nonearly responders (group A). Almost all early responders had high anti-HBs titer (≥100 mIU/mL) after 1 GSK3 inhibitor month. This supported the notion that early responders 上海皓元医药股份有限公司 maintained immune memory and thus would have more robust immune responses to HB vaccine compared with the nonearly responders. We also found that the levels of the early response were not critical. Those with early anti-HBs between 10 and 100

mIU/mL (group B) and anti-HBs ≥100 mIU/mL (group C) behaved similarly in the subsequent anti-HBs responses. Hence, we believe that a conversion of anti-HBs from <10 mIU/mL to ≥10 mIU/mL 7-10 days after one dose of the HB vaccine booster could be defined as the presence of immune memory. Participants with an early booster response had titers up to 20 times higher than those who could not mount an early response after 1 month. These findings suggest that when immune memory was present, anti-HBs responses could be induced as early as 1 week following a booster and such responders are likely to have protective titers after a single dose and may not need further doses. However, subjects who do not mount an anamnestic response might still be able to mount a protective response to infection. The nonresponding rates to plasma-derived HB vaccines have been estimated to be less than 10% according to previous studies.7, 19 Some of those who had a slow or no response to the second course of HB vaccines might be nonresponders but they are few. In our study, 94.