2026 Eastern States Conference

Title
Evaluation of pneumococcal antibody titer levels in allogeneic hematopoietic stem cell transplant 
 
Authors
Robyn Turner, PharmD; Rebekah Dyer, PharmD, BCPS 
 
Learning Objective  
Develop a plan for subsequent pneumococcal immunizations based on pneumococcal antibody titer levels. 
 
Background/Objective
To determine the number of allogeneic hematopoietic stem cell transplant (HSCT) recipients with protective pneumococcal antibody titer levels of ≥0.35 μg/mL at Virginia Commonwealth University Health System (VCUHS). 
 
Methods
This was a single-center, retrospective, observational project evaluating pneumococcal antibody titer levels from January 2022 to December 2024.  Adult patients who underwent an allogeneic HSCT, received at least one dose of pneumococcal polysaccharide vaccine (PPSV) or pneumococcal conjugate vaccine (PCV), and had at least one pneumococcal antibody titer panel drawn were included.  The World Health Organization defines protective levels as ≥0.35 μg/mL for PCV serotypes, while expert opinion suggests ≥1.3 μg/mL for PPSV serotypes.  At VCUHS, a level of ≥1.3 μg/mL has been considered protective, regardless of the serotype.  Because thirteen of fourteen serotypes in the VCUHS titer panel are contained in PCV20, this project evaluated whether the lower threshold confers protection.  Protective antibody titer levels were defined as 75% (10/13) of serotypes meeting either threshold.  Data were collected from the electronic medical record and the Virginia Immunization Information System.   
 
Results
There were forty-five patients included.  Using antibody titer level threshold of ≥1.3 μg/mL and ≥0.35 μg/mL, 10 patients (22%) and 26 patients (57%) had protective antibody titer levels, respectively (p=0.0024).  One patient had confirmed invasive pneumococcal disease (IPD).  Although the primary objective of patients with protective antibody titer levels at the lower threshold compared to the higher threshold met significance, the small sample size limited the ability to evaluate potential confounding factors associated with meeting the threshold for protective antibody titer levels. 
 
Conclusion(s)
The number of patients with protective antibody titer levels based on the lower threshold of ≥0.35 μg/mL was significant.  This suggests that the lower threshold may be appropriate to confer protection against IPD in patients who underwent an allogeneic HSCT because only one patient had confirmed IPD.  Updating internal guidance documents to define protective antibody titer levels using the lower threshold may be warranted.   
 
Self-Assessment Question 
 
Why was it important to evaluate the lower threshold of ≥0.35 μg/mL in this project? 
 
A. It is the standard used for all pneumococcal serotypes at VCUHS 
B. It is the established threshold for PPSV serotypes
C. Thirteen of fourteen serotypes in the VCUHS titer panel are contained in PCV20
D. It eliminates the requirement for pneumococcal revaccination in HSCT recipients 
 
Disclosures
The authors and contributors have no conflicts of interest to disclose.