To evaluate the effect of tixagevimab/cilgavimab (T/C) on the incidence of COVID-19 in patients with multiple sclerosis (pwMS) and neuromyelitis optica spectrum disorder (pwNMOSD).

AntiCD20 therapy, such as rituximab or ocrelizumab, effectively treats pwMS and pwNMOSD but negatively affects the immune response to COVID-19 vaccination. One strategy to protect these patients is using T/C as pre-exposure prophylaxis.

Data were collected in two MS centers between March 1, 2020 and December 31, 2022. Adult pwMS and pwNMOSD: 1. treated with antiCD20 at least six months before T/C, or at least from February 1, 2022 in the control group (CG), 2. who were already on antiCD20 at the time of vaccination or COVID-19; 3. who were on antiCD20 at least 100 days after T/C, or at least 90 days after August, 1, 2022 in the CG, were included.

Using propensity score matching 1:1, 47 patients who received T/C were matched with those who did not receive T/C (n=341) based on age, MS/NMOSD duration, and number of vaccine doses. None of the T/C patients and three in the CG developed a COVID-19 between 10–100 days after receiving T/C, August, 1, 2022 respectively (without significant difference; p=0.242). Using a non-informative Bayesian prior, the median relative risk of COVID-19 after T/C was 7.6% (95% CrI 0.02–115.9%). The posterior probability of risk difference lower than zero was 96.4%. Using an informative prior (based on the registration study of Evusheld), the median relative risk of COVID-19 after T/C was 20.2% (95% CI 8.4-43.8%). The posterior probability of the risk difference lower than zero was 100%.

This work highlights the possible good efficacy of T/C in antiCD20 treated pwMS and pwNMSOD. However, given the low frequency of COVID-19, the results of this pilot analysis must be interpreted with caution.