Effect of cladribine on COVID-19 serology responses following two doses of the BNT162b2 mRNA vaccine in patients with multiple sclerosis

Background: multiple sclerosis (MS) patients are treated with immunomodulatory treatments that can influence their ability to develop a protective antibody response to the SARS-CoV-2 vaccine. Vaccine efficacy is important for treatment decision and for patients’ reassurance. The main objective is to assess antibody response to SARS-CoV-2 vaccine in MS patients treated with cladribine. Methods: Serology response was tested in 97 participants, 67 MS patients and 30 healthy controls (HCs), using two independent methods, 2–3 weeks following the second dose of the BNT162b2 vaccine. Results: HCs (n = 30) and MS patients treated with cladribine (n = 32) had 100% positive serology response against the SARS-CoV-2 spike protein following the second vaccine dose (mean S1/S2-IgG and RBD-IgG:284.5 ± 104.9, 13,041±9411 AU/mL and 226.3 ± 121.4, 10,554±11,405 AU/mL respectively). Comparable findings were observed for untreated MS patients, and interferon beta-1a-treated MS patients (mean S1/S2-IgG: 282.1 ± 100.1, 276.9 ± 94.31 AU/mL respectively). No correlation was found between lymphocyte counts, treatment duration, or time between cladribine dose and vaccination, and serology response or antibody titers. Conclusion and relevance: Cladribine treated MS patients are able to produce antibodies to the SARS-CoV-2 mRNA vaccine. In the era of the COVID-19 pandemic, it is reassuring and important for both patients and physicians and will allow to develop consensus guidelines.