Humoral immune response to SARS-CoV-2 third vaccination in patients with multiple sclerosis and healthy controls: A prospective multicenter study.

Background: Third vaccination against SARS-CoV-2 is recommended for patients with multiple sclerosis (pwMS), usually six months after the last vaccination.

Methods: In this prospective multicenter study on 292 pwMS and 46 healthy controls (HC), who had all received two vaccinations prior to study enrollment, SARS-CoV-2 IgG response was measured in the month before and 2-4 months after third vaccination. PwMS were categorized as follows: untreated (N-DMT, n = 32), receiving disease-modifying therapy (DMT) with expected humoral response (er-DMT: interferon-beta preparations, glatiramer acetate, dimethyl fumarate, teriflunomide, natalizumab, cladribine, alemtuzumab; n = 120) or no expected humoral response (nr-DMT: S1PMs, CD20mAb; n = 140).

Results: PwMS on nr-DMT had significantly lower median antibody levels before (12.1 U/ml [0.4-2500]) and after third vaccination (305 U/ml [0.4-2500]) in comparison to other groups (p<0.001). We did not find differences in antibody levels after homologous (n = 281; 2500 [0.4-2500]) and heterologous (n = 57; 2500 [0.4-2500]) vaccination regime regardless of the DMT group. The DMT group (β= -0.60; 95% CI -1195.73, -799.10; p<0.001) was associated with antibody levels after third vaccination, while time to revaccination (6 months [1-13]) was not. After third vaccination, seropositivity was reached in 75.8% and 82.2% of pwMS on anti-CD20 mAbs and S1PMs, respectively. Complete B-cell depletion significantly decreased the probability of seroconversion even after the third vaccination (OR 0.14; p = 0.021), whereas time interval to last DMT intake and time to revaccination did not. Twenty-two patients reported a SARS-CoV-2 infection (3 N-DMT, 9 er-DMT, 10 nr-DMT), one being asymptomatic and the rest having a mild course.

Conclusion: Humoral response to SARS-CoV-2 third vaccination in pwMS is excellent. While reduced by S1PMs and CD20mAb, protective response is still expected in the majority of patients.