From the Guidelines

Acute infections can exacerbate Multiple Sclerosis (MS) symptoms and trigger relapses.

Acute infections can induce immunological responses and trigger immunological reactions, leading to MS relapses or pseudo-relapses 1.
Patients with MS are at increased risk of severe infections, complications, and mortality, making vaccination against infections like Covid-19 vital for this population 1.
However, some disease-modifying therapies (DMTs) used to treat MS can reduce the antibody response following vaccination, affecting the safety and efficacy of vaccines 1.

Vitamin D has been studied for its potential to reduce MS relapse rates, but current evidence is inconclusive 1.
Some studies suggest that vitamin D may have immunomodulatory effects, increasing lymphocyte proliferation and reducing pro-inflammatory cytokines, but high-quality evidence is lacking 1.

Patients with MS should be monitored closely for signs of infection and relapse, especially when switching therapies or starting new treatments 1.
Frequent MRI scanning should be performed in patients who switch therapies to detect resurgent MS disease activity and adverse effects such as opportunistic infections 1.

From the Research

Acute infections, particularly those of viral origin, have been linked to the exacerbation of Multiple Sclerosis (MS) symptoms 2.
Studies have shown that upper respiratory infections, gastrointestinal infections, and urogenital tract infections can trigger MS exacerbations 3, 4.
The exact mechanisms by which infections trigger MS exacerbations are not fully understood, but it is thought that they may modulate the neuroimmunological system of genetically susceptible individuals 3, 4.

Several viruses, including Epstein-Barr virus, human herpesvirus 6, and human endogenous retroviruses, have been proposed as potential triggering agents for MS 5, 6.
These viruses can establish lifelong infections with periods of reactivation, which may be linked to the relapsing nature of MS 6.
The efficacy of interferon therapy in MS patients also supports the idea of a viral etiology for the disease 6.

Bacterial infections, such as those caused by Chlamydia pneumoniae and Staphylococcus aureus, have also been linked to MS exacerbations 3.
However, the evidence for a role of bacterial infections in MS is not as strong as that for viral infections 3, 4.

There is currently no sufficient evidence to support associations between standard vaccination policies and increased risk of MS 5.
MS patients treated with immunomodulatory therapies may have a lower benefit from viral and bacterial vaccination 5.