Large Majority of Stem Cell Transplant Recipients Show Antibody Response to COVID-19 Vaccination

Most stem cell transplant recipients who were fully vaccinated against COVID-19 had a positive anti-spike antibody response after the second dose, a new study found.

The single-center cohort study, published in JAMA Network Open, included 117 allogeneic hematopoietic stem cell transplant (HSCT) recipients who received the Pfizer-BioNTech COVID-19 vaccine between Jan. 20 and April 17 at Nantes University Hospital in France.

The study found that 83% of participants had positive antibody responses after two doses of the vaccine, a promising result for a population at high risk of morality from COVID-19.

“The preliminary findings reported here are reason for optimism, yet there is clearly room for improvement and much more to learn about preventing and managing COVID-19 after allogeneic HCT,” Joshua A. Hill, MD, an assistant professor at the Fred Hutchinson Cancer Research Center and the University of Washington wrote in an associated commentary.

The participants had no active graft-vs-host disease, median age was 57, 60% were male and they received two doses of the Pfizer-BioNTech COVID-19 vaccine a median of 22 days apart. The vaccine was administered more than three months after the stem cell transplant.

Antibody responses were tested using the Elecsys anti–SARS-CoV-2-S assay at the time of the second injection and again about 1 month afterward (median interval of 35 [18-77] days). At the time of the second injection, 63 participants (54%) had a positive anti-spike antibody response, defined as titers greater than or equal to 0.8 U/mL. The median IgG titer was 15.8 U/mL, and four participants had titers ofmore than 250 U/mL. After the second injection, 97 patients (83%), had positive IgG titers, and 72 (62%) patients reached the highest IgG titer of more than 250 U/mL.

“This is much more than the 54% rate of seroconversion that has been reported after 2 doses in solid-organ transplant recipients and compares favorably with data obtained in patients treated for solid tumors, for whom a 95% of response rate was obtained after the second dose,” the study authors wrote. “This humoral response is, however, only 1 marker of immunity, and allogeneic HSCT recipients will likely have differences in T cell reactivity that should be explored.”

Absence of antibody response was associated with haplo transplant, recent HSCT within the past year, lymphopenia and receipt of immunosuppressive treatment or chemotherapy at the time of vaccination.

The COVID-19 vaccine was found to be safe, with only grade 1 or 2 adverse events reported among 48% of participants after the first dose and 39% after the second dose, similar to those of a healthy cohort. No COVID-19 cases were reported among participants at a median follow-up of 58 days.

Hill noted that the vaccination should be included among efforts to protect against COVID-19 after allogeneic HCT, including avoiding high-risk exposure, masking, hand hygiene and ensuring that close contacts are vaccinated.

“The available data collectively demonstrate that SARS-CoV-2 vaccination should continue to be a priority after allogeneic HCT but is only one aspect of a broader management strategy,” he wrote.

The efficacy of COVID-19 vaccines in cancer patients, transplant recipients and other immunocompromised populations has been a focus of recent research.

A pair of recent studies found that patients with blood cancers may have impaired antibody response to COVID-19 vaccines.

Another recent study found that 94% of cancer patients developed antibodies to COVID-19 after vaccination. Patients with hematological malignancies had significantly reduced humoral response compared with those with solid tumors.