SARS-CoV-2 pandemic as a model to assess the relationship between intercurrent viral infections and disease activity in Multiple Sclerosis: A propensity score matched case-control study

INTRODUCTION: An association between intercurrent viral respiratory infections and exacerbations of Multiple Sclerosis (MS) disease activity has been proposed by several studies. Considering the rapid spread of SARS-CoV2 worldwide and the systematic effort to immediately detect all incident cases with specific diagnostic tests, the pandemic can represent an interesting experimental model to assess the relationship between viral respiratory infections and MS disease activity. AIMS AND METHODS: In this study, we have performed a propensity score matched case-control study with a prospective clinical/MRI follow-up, on a cohort of relapsing-remitting MS (RRMS) patients who tested positive for SARS-CoV2 in the period 2020–2022, with the aim to evaluate if the SARS-CoV2 infection influences the short-term risk of disease activity. Controls (RRMS patients not exposed to SARS-CoV-2, using 2019 as the reference period) were matched 1:1 with cases for age, EDSS, sex and disease-modifying treatment (DMT) (moderate efficacy vs high efficacy). Differences in relapses, MRI disease activity and confirmed disabilty worsening (CDW) between cases in the 6 months following the SARS-CoV-2 infection, and controls in a similar 6 months reference period in 2019 were compared. RESULTS: We identified 150 cases of SARS-CoV2 infection in the period March 2020 - March 2022, out of a total population of approximately 1500 MS patients, matched with 150 MS patients not exposed to SARS-CoV2 (controls). Mean age was 40.9 ± 12.0 years in cases and 42.0 ± 10.9 years in controls, mean EDSS was 2.54±1.36 in cases and 2.60±1.32 in controls. All patients were treated with a DMT, and a considerable proportion with a high efficacy DMT (65.3% in cases and 66% in controls), reflecting a typical real world RRMS population. 52.8% of patients in this cohort had been vaccinated with a mRNA Covid-19 vaccine. We did not observe a significant difference in relapses (4.0% cases, 5.3% controls; p = 0.774), MRI disease activity (9.3% cases, 8.0% controls; p = 0.838), CDW (5.3% cases, 6.7% controls; p = 0.782) in the 6 months after SARS-CoV-2 infection between cases and controls. CONCLUSION: Using a propensity score matching design and including both clinical and MRI data, this study does not suggest an increased risk of MS disease activity following SARS-CoV-2 infection. All MS patients in this cohort were treated with a DMT, and a considerable number with a high efficacy DMT. These results therefore may not be applicable to untreated patients, for which the risk of increased MS disease activity after SARS-CoV-2 infection may not be excluded. A possible hypothesis explaining these results could be that SARS-CoV2 is less prone, compared to other viruses, to induce exacerbations of MS disease activity; another possible interpretation of these data might be that DMT is able to effectively suppress the increase of disease activity triggered by SARS-CoV2 infection.