While it is recommended that patients with multiple sclerosis (MS) be vaccinated against COVID-19, it is unknown what the vaccine response is in MS patients treated with fingolimod, an agent which modulates the humoral response. We aimed to characterize the immune response to the COVID-19 vaccine in MS patients treated with fingolimod and to explore which factors influenced response.

We collected the following data from 59 MS patients treated with fingolimod and vaccinated against COVID-19: age, sex, duration of treatment, number of vaccine doses, date of last vaccination, type of vaccine, lymphocyte count, history of COVID-19, and serology to measure the vaccine response. We used Student's t-test and Chi² test to see whether there was a relationship between these variables and seropositivity. A multivariate logistic regression model was used to identify factors influencing the serology result. A multivariate linear regression model was used to identify factors influencing the antibody titer.

Twenty-eight participants (47%) developed a positive serology. Age (P<0.001) and the duration of treatment (P=0.002) were significantly related to seropositivity. Gender (P=0.73), number of vaccinations (P=0.78), lymphocyte count (P=0.46), and the time between the last vaccine dose and blood sampling (P=0.84) were not significant variables. Multivariate analysis using logistic regression (n=59) showed that age (P=0.003, RR = 2.28, 95%CI = 1.28, 4.07) and duration of treatment (P=0.04, RR=1.91, 95%CI=1.04, 3.50) were significantly and independently correlated with COVID serology. Multivariate linear regression analysis of the antibody titer (n=59) found the duration of treatment to be significant (P = 0.015), but not age (P = 0.53). After removing three outliers, age (P = 0.005, RR=6.82, 95%CI=1.66, 27.98) and duration of treatment (P = 0.008, RR=5.12, 95%CI=1.24, 21.03) were significantly correlated with the antibody titer.

COVID-19 seropositivity was present in 47% of our sample of 59 MS patients on fingolimod. A strong relationship was found between antibody development, age, and duration of treatment, as well as between antibody titer and age and duration of treatment.