Assessment of coronavirus disease 2019 mRNA vaccine response in kidney transplant recipients

Kidney transplant recipients are vulnerable to developing severe coronavirus disease 2019 (COVID-19) infection. Although mRNA vaccines have significantly improved outcomes, seropositivity rates remain variable in immunosuppressed patients. This study aimed to evaluate the antibody response to COVID-19 mRNA vaccines, identify factors affecting immunogenicity, and examine the association between antibody titers and subsequent SARS-CoV-2 infection and COVID-19-related hospitalization among kidney transplant recipients. We retrospectively studied 372 adult kidney transplant recipients who received two doses of COVID-19 mRNA vaccine after transplantation and had anti-SARS‑CoV‑2 spike protein receptor-binding domain antibodies measured ≥ 14 days after the second dose and prior to receiving a third dose. We categorized patients based on previous COVID-19 infection, post-vaccination antibody status (seropositive or seronegative), and antibody titers (low or high). Factors associated with poor vaccine response (seronegativity) and with high antibody titers (antibody titer ≥ 121 U/mL) were determined using multivariable regression models. The proportion of patients with subsequent COVID-19 infection was higher in the seronegative group than in the seropositive or previous infection groups (36% vs. 26% vs. 13%, respectively; P = 0.02). Multivariable regression analysis revealed higher odds of poor response to the mRNA vaccine among patients aged > 52 years compared with those aged ≤ 52 years (aOR = 1.94; 95% CI: 1.12–3.36; P = 0.018). Lower odds were observed among male patients (aOR = 0.43; 95% CI: 0.24–0.77; P = 0.004) and those taking azathioprine (aOR = 0.26; 95% CI: 0.07–0.91; P = 0.035). The proportion of patients with subsequent COVID-19 was also higher in the low-antibody group than in the high-antibody group (33% vs. 20%; P = 0.02). Multivariable logistic regression analysis showed lower odds of high SARS-CoV-2 antibody titers among patients aged > 51 years compared with those aged ≤ 51 years (aOR = 0.43; 95% CI: 0.24–0.75; P = 0.003). Higher odds were observed among those of African race (aOR = 2.82; 95% CI: 1.11–7.16; P = 0.03) and South Asian race (aOR = 2.27; 95% CI: 1.08–4.75; P = 0.03) compared with Middle Eastern recipients. Understanding the immunologic response to the SARS-CoV-2 vaccine in kidney transplant recipients is essential for preventing potentially life-threatening infection. Furthermore, identifying transplant recipients with a low vaccine-induced antibody response may help guide the development of individualized immunization strategies.