Objectives Anti-CD20 therapy for inflammatory demyelinating CNS disorders increases SARS-CoV-2 incidence and severity, demonstrating the value of vaccination in this group. Low vaccine seroconver- sion is observed in those on anti-CD20 therapy. A 12-week interval following anti-CD20 infusion before vaccination and a 2-4-week interval following vaccination before infusion is recommended. Patients are eligible for a third dose and booster. Infusions are given 6-monthly. This schedule cannot be followed without treatment delays, forcing prescribers to prioritise vaccination versus risk of disease progression. We aimed to assess the provision of these recommendations in NHS Tayside by quantifying SARS-CoV-2 incidence and severity.

Methods All patients receiving anti-CD20 therapy for inflammatory demyelinating CNS disorders were included. SARS-CoV-2 infection incidence was quantified, severity was measured by engagement with secondary care. Vaccine uptake and treatment delays were measured.

Results 66 patients were included. 51 received ocrelizumab (27 RRMS, 24 PPMS). 15 received rituximab

(8 NMOSD, 3 NMOSD/MS overlap, 4 RRMS). 13 patients contracted COVID. 5 patients required hospital admission. 2 had COVID-pneumonitis associated respiratory failure requiring HDU admission. 2 contracted COVID while unvaccinated. Only 3 had received 4 vaccine dosages, 2 of which tested positive due to PCR screening pre-infusion.

33 (67.3%) patients had treatment delays receiving infusions greater than 6-months apart.

Conclusions Patients receiving anti-CD20 therapy for inflammatory CNS disorders have been complex to manage during the pandemic. Guidance regarding a third primary dosage came late in the pandemic.