New data shed light on the durability of antibody responses to SARS-CoV-2 vaccines and the impact of booster doses for patients with cancer undergoing systemic therapy or who have received a stem cell transplant (SCT).
In a cross-sectional study of 453 such patients, anti–SARS-CoV-2 spike protein receptor binding domain (anti-RBD) antibodies peaked 1 month after the second dose of an mRNA vaccine and remained stable over the next 6 months.
Notably, compared with the primary vaccine course, patients experienced a 20-fold increase in anti-RBD antibodies after the third vaccine dose, “indicative of a brisk anamnestic response from memory B cells,” Qamar Khan, MD, a medical oncologist at the University of Kansas Medical Center, Kansas City, and colleagues report.
The study appeared online in JAMA Oncology.
Given the risk of poor outcomes among patients with cancer and recipients of SCTs who get COVID, Dr. Khan and colleagues wanted to understand the durability of the antibody response to COVID vaccines in this population.
Among the 453 patients enrolled in the study, 70% had solid tumors and 30% had hematologic malignancies. Just over 40% were receiving chemotherapy, 16% were receiving immunotherapy, 14% were receiving a targeted oral agent, 5% were receiving chemoimmunotherapy, and 25% had received an SCT.
Regarding vaccine type, 61% received the Pfizer-BioNTech mRNA vaccine, 36% received the Moderna mRNA vaccine, and 4% got the Janssen/Johnson & Johnson vaccine. The mean age of the cohort was 60.4 years; 56% were women.
Prior to vaccination, the geometric mean titer (GMT) of anti-RBD antibodies for all patients was 1.7; it increased to 18.65 2 weeks after the first dose.
At 1 month after the second mRNA dose (or 2 months after the Johnson & Johnson vaccine), GMTs of anti-RBD antibodies reached 470.38 and then decreased to 425.8 at 3 months after the second dose (or 4 months after the Johnson & Johnson vaccine). Patients who were male, older than 65 years, and who had been diagnosed with a hematologic malignant tumor were more likely to have lower anti-RBD GMT 3 months after the second vaccine dose.
GMTs subsequently increased to 447.23 6 months after the second dose (7 months for Johnson & Johnson).
One month after the third dose, GMTs of anti-RBD antibodies rose to 9,224.85 – more than 20 times the previous GMT value.
According to the investigators, roughly 80% of these patients remained above the threshold of an anti-RBD level of 100 U/mL or higher at 6 months.
“While still an arbitrary cutoff, an anti-RBD level of 100 U/mL or higher has been associated with protection and has been used to evaluate the effectiveness of a third dose of an mRNA vaccine in a randomized clinical trial of patients who received a solid organ transplant,” Dr. Khan and colleagues write.
“Although more data are needed to confirm this level as protective, if established, anti-RBD can potentially be used to prioritize additional vaccine doses, especially in regions of the world with limited vaccine resources,” the authors conclude.
The study was supported in part by the University of Kansas Cancer Center and the Investigator Initiated Steering Committee, by a grant from the National Institute of General Medical Sciences, and a University of Kansas Cancer Center Support Grant from the National Cancer Institute. Dr. Khan reported no relevant financial relationships.
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