With the implementation of hepatitis B surface antigen tests that have greater sensitivity, facilities have identified an increased number of blood donors that have confirmed positive for hepatitis B surface antigen after receiving a hepatitis B virus vaccination. This increased reactivity in donors without specific risk factors and who are nonreactive for all other HBV markers, including antigen to hepatitis B core antibody and HBV DNA (if this test was performed), is most likely due to the vaccine, which typically contains approximately 10 micrograms of HBsAg as the immunizing dose. When diluted in 5 liters of blood — the volume in the human body — the concentration of HBsAg in plasma would be 2-4ng/mL (hematocrit dependent), which is easily detectable by contemporary assays.
Due to the likelihood of vaccine-induced confirmed-positive HBsAg test results, many facilities practice temporary deferral of donors following HBV vaccination (any of the three doses) for between seven and 21 days. While a specific deferral period cannot be determined until ongoing retrospective and prospective studies are completed, it is apparent that a seven-day deferral is not long enough when using assays with HBsAg-detection levels of approximately 0.1 ng/mL. A deferral period of 14 to 21 days is likely more appropriate. The choice of the actual number of days is up to the discretion of the facility, based on their assessment of balancing unnecessary deferral with the risk of finding an HBV vaccine-induced, HBsAg confirmed-positive donor.
Once the vaccine-induced HBsAg has cleared a donor’s system, the donor should be eligible for re-entry into the blood donor pool. However, the re-entry process requires approval from the Food and Drug Administration. To help facilities choosing to re-enter these donors, AABB has developed a template that may be used by facilities on a case-by-case basis when requesting re-entry under the provisions of 21 CFR 610.41(b). Only donors who received the vaccine prophylactically and not due to a known exposure as defined by AABB standards or FDA regulations are eligible for re-entry.