Live Immunization Practices for Chronically Transfused Pediatric Patients

Introduction: Children with hemoglobinopathies often require chronic transfusion as a part of their care. The Canadian Immunization Guide, the National Advisory Committee on Immunizations, and the Centre for Disease Control recommend avoidance of live vaccination for a period following blood product transfusion. The literature indicates that human derived blood products contain significant amounts of antibodies to infectious agents that are prevalent in the general population, due to natural disease or vaccination of the donor, such as the measles virus and varicella zoster virus. The recommended time interval between packed red blood cell (PRBC) transfusion and live vaccination was extrapolated from a study which assessed vaccine responses after administration of Intravenous immune globulin. If practitioners adhere to guidelines, many chronically transfused pediatric patients would not be eligible to receive live vaccinations due to concerns of non-response to the vaccine. Thecomposition of blood products has changed over time and current immunization recommendations may not reflect the blood products being utilized today. Specifically, the amount of residual plasma in PRBCs has been reduced substantially, reducing passive antibody concentration and likely reducing interference in the immune response. To our knowledge, the immune response to live vaccines has not been formally studied in pediatric patients who undergo chronic transfusion with PRBCs. We aimed to determine the current live immunization practices of health care providers (HCPs) caring for chronically transfused pediatric patients.

Hypothesis: Is there heterogeneity in the live immunization practices of North American Pediatric HCPs who care for chronically transfused children?

Methods: The study was approved by the University of Alberta Research Ethics Board. A cross-sectional online survey was circulated to North American hematology HCPs. The survey was peer-reviewed by 7 practitioners prior to distribution for content and face validity with 3 versions before final approval and distribution. The survey was distributed via the Canadian Hemoglobinopathy Association (CanHaem,186 members) and the American Society of Pediatric Hematology/ Oncology (ASPHO, 1991 members) listservs. Responses were collated from June 2017-July 2017 in a REDcap database. Data was analyzed using descriptive statistics.

Results: There were 60 respondents total. 60% of HCPs were from the U.S.A., and 70% cared for 1-19 patients meeting study criteria. The majority had 1-10 patients who travelled to measles endemic countries annually, and 33% of HCPs reported there had been a local outbreak of Measles, Mumps, Rubella or Varicella (MMRV) within the past year. Despite this, 50% were unaware of the MMRV immune-status of their patients. Eighty-seven percent of HCPs continued to administer live vaccinations as per the routine immunization schedule. Less than 10% had a protocol for the care of chronically transfused patients, and <25% complete pre-and-post vaccination serologies to assess immune-status in the transfused population. Respondents reported various follow-up strategies, including education of patients (40%), documentation of potential susceptibility to MMRV (15%), and education of the HCP's administering live vaccines (20%). Only 24/55 (44%) of respondents were aware of the recommendation to avoid live vaccinations in transfused patients, and 44% of respondents did not have a follow-up strategy for chronically transfused patients regarding immune-status.

Conclusion: Live immunization practices for chronically transfused pediatric patients vary across North America. Many HCPs are unaware of the recommendations around avoidance of live immunizations post transfusion. Most respondents immunize their chronically transfused pediatric patients as per the routine schedule, but the immune-status post-vaccination is often unknown. Given changes to the processing of blood products over the last several decades, further research is needed in this area. Determination of pre-and-post-immunization serologies may help to establish the response of chronically transfused patients to live vaccinations, and allow for the development of evidence-based guidelines for live-immunization of this vulnerable patient population.