Learning Objectives for this Presentation:
By the end of the presentation, participants will be able to understand how PVST timing can affect HBV immune status test results

Background:
To ensure immunity to hepatitis B virus (HBV), PVST for anti-HBs is recommended at age 9-18 months for infants of HBsAg-positive mothers who have completed the HBV vaccine series. However, delayed PVST can result in false negative anti-HBs test results.

Objectives:
To determine if increased time between completion of the HBV vaccine series and PVST was associated with an increase in negative anti-HBs test results.

Methods:
We examined a retrospective cohort of infants born between 2000-2005 who were enrolled in the California Perinatal Hepatitis B Prevention Program and compared PVST timing after vaccination between infants who were anti-HBs negative/HBsAg-negative and those who were anti-HBs positive/HBsAg-negative.

Results:
8,064 infants born during the study period received PVST for anti-HBs at 9 months of age or older. 504 (6.3%) were anti-HBs negative/HBsAg-negative; of these 6 (1.2%) received PVST <2 months, 405 (80.4%) 3-12 months, 48 (9.5%) 13-18 months and 26 (5.2%) 19-30 months after vaccination. Of the 7,560 (93.8%) anti-HBs positive/HBsAg-negative infants, 104 (1.4%) received PVST <2 months, 6,804 (90.0%) 3-12 months, 356 (4.7%) 13-18 months and 179 (2.4%) 19-30 months after vaccination. Anti-HBs negative infants had significantly longer intervals between HBV vaccine series completion and PVST (p<0.001).

Conclusions:
A longer interval between completion of the HBV vaccine series and PVST was associated with an increase in negative anti-HBs test results among infants born to HBsAg infected mothers. Some of these negative results may reflect waning of detectable immunity. Performing PVST as soon as possible after the age of 9 months minimizes the risk of false negative anti-HBs test results and additional HBV vaccination in these infants.