BACKGROUND/AIMDisease-modifying therapy (DMT) has led to added challenges in the management of people with multiple sclerosis (pwMS) during the COVID-19 era. It can reduce relapse in MS or slow down disease progression, but some DMTs can increased risk of infection. The aim of study was to evaluate risk and severity of COVID-19 in pwMS.METHODSThe examined group of pwMS were divided in group treated with IFN-β1a, group treated with ocrelizumab and untreated group. The examination included impact of age, gender, duration of MS, type of MS, vaccination status and Expanded Disability Status Scale (EDSS) on the risk and severity of COVID-19 infection. A diagnosis of COVID-19 in pwMS was confirmed by positive polymerase-chain-reaction (PCR) or antigen test.RESULTSOut of 207 pwMS, 82 patients were treated with ocrelizumab, 63 with IFN-β1a, while 62 patients were untreated pwMS. The average duration of the MS was longer in the group of patients treated with ocrelizumab than in the group treated with IFN-β1a (p < 0.05). EDSS was higher in the ocrelizumab group compared to the other two groups (p < 0.001). Untreated (more often unvaccinated) had the same COVID frequency as ocrelizumab-treated (more vaccinated, but higher EDSS). The multivariate logistic regression model indicated that administration of IFN-β1a reduces the risk of COVID-19 infection (p = 0.001, OR = 0.381, 95% CI 0.602-0.160). The use of both DMTs, driven mainly by the IFN-β1a effect, reduces the risk of moderate and severe COVID-19 (p < 0.05, OR = 0.105, 95% CI 0.011-0.968).CONCLUSIONThis study provides evidence that IFN-β1a can reduce the frequency of COVID-19 infection and that two DMTs, driven mainly by the IFN-β1a effect, do not increase the risk of moderate/severe COVID-19.