Impact of the Modifications of Environmental Exposures and Health Care Access During COVID-19 Lockdown on the Risk of Multiple Sclerosis Clinical Relapse or Clinical Worsening

Multiple sclerosis (MS) is a common autoimmune disease of the central nervous system. The repetition of relapses and their severity will lead in the long term to the accumulation of disability. The risk factors for relapses are still poorly understood, but it is suspected that air pollution and seasonal viral infections may increase the risk of relapse.

The Sars-Cov-2 virus pandemic has abruptly disrupted the daily environment, to date three lock-down periods have been implemented, in France, to limit the spread of COVID 19, the first was from March 17 to May 11, 2020, the second was less strict from October 30 to December 15, 2020, and the third began April 3, 2021. The reduction in road traffic during the first containment was accompanied in Ile de France by a 30 to 50% decrease in fine particulate matter and nitrogen oxide air pollution compared to the previous year. The confinements and the generalized application of barrier measures have also been associated with a clear decrease in the circulation of seasonal viruses, in particular influenza and viral gastroenteritis viruses, compared to the previous year.

To date, the impact of measures to prevent the spread of the Sars-CoV-2 epidemic on the risk of MS relapse has not been studied. However, these periods offer a unique opportunity to assess, in a quasi-experimental model, the impact of air pollution and viral infections on the risk of MS relapse, in a context where these factors have shown large variations compared to the usual seasonal values observed.

The pandemic has also had a profound impact on the health care system, with the corollary that patients with chronic pathologies have had difficulty accessing care, as hospital structures have had to deal with an unprecedented crisis, resulting in the de-scheduling of non-urgent procedures and great difficulty in accessing in-person consultations. Numerous uncertainties concerning the risk of severe COVID-19 in patients treated with immune-modulators or immune-suppressors have led to the suspension or delay of the initiation of immuno-active treatments to prevent the aggravation of the disease. To date, no study has evaluated the impact of changes in the management of MS patients during this particular period and to assess the impact on the progression of neurological disability.

The primary objective of the study will be to determine the impact of environmental risk factors (air pollution, exposure to seasonal viruses) and health care access on the risk of clinical MS relapse, in the context of the lockdown periods, compared to periods prior to the COVID-19 pandemic.