Vaccines Not Associated With MS Flare-Ups That Require Hospitalization

Among patients with multiple sclerosis (MS), there is no association between severe MS flare-ups and vaccine exposure, according to study findings published in JAMA Neurology.

Infections in patients with MS increase the risk for flare-ups and symptom severity. Accordingly, international guidelines recommend vaccination for patients with MS. However, vaccination hesitancy exists among patients with MS due to inconclusive evidence linking vaccination to the onset of overt autoimmune symptomology.

For the study, researchers sought to clarify whether vaccinations are associated with severe flare-ups requiring hospitalization in patients with MS.

The System of National Health Databases (SNDS) registry, containing deidentified information from more than 99% of French residents, was used to identify a cohort of 106,523 patients with MS (mean age, 43.9; 71.8% women). Flare-ups were defined as hospitalizations lasting at least 1 day with either a specific MS or MS disorder in the discharge diagnosis. A minimum of 120 days was needed between flare-ups to be considered separate events. Vaccination was confirmed via claims within the SNDS dispensing database. A nested case-crossover analysis was performed to evaluate the association between MS flare-ups and vaccine exposure.

Participants included 33,864 patients with MS, with 54.6% of patients receiving a vaccine at any time during the 11 years of the trial, including 45.3% after enrolling in the MS cohort. The most common vaccinations included diphtheria, tetanus, poliomyelitis, pertussis, and Haemophilus influenzae (DTPPHi; 30.3%), influenza (19.2%), and pneumococcus (7.0%).

A total of 33.1% of patients were hospitalized with a flare-up at least once during follow-up. Within 60 days of exposure to any vaccine, the researchers found no increase in hospitalization for a flare-up (adjusted odds ratio [aOR], 1.00, 95% CI, 0.92-1.09). The researchers found this was true for these vaccines: DTPPHi (aOR, 0.95, 95% CI, 0.82-1.11), influenza (aOR 0.98, 95% CI, 0.88-1.09), and pneumococcal (aOR, 1.20; 95% CI, 0.94-1.55). Similarly, no associations were found according to sex or age group.

This association remained unchanged when both 30-day and 90-day risk windows were applied. However, during the 90-day time window, there was a slight increase in aOR for the pneumococcal vaccine that was statistically significant (aOR, 1.59; 95% CI, 1.27-1.99). The researchers noted that although there was no association observed between vaccine exposure and MS flare-ups requiring hospitalization, “Nevertheless, the study cannot completely rule out the existence of a small risk, particularly in the case of the pneumococcal vaccine.”

One limitation of the SNDS database is that clinical information is conveyed via hospital diagnosis codes and drug dispensing records instead of direct patient interactions; however, authors noted the benefit of using the SNDS database, stating that, “Because health insurance in France is universal and access to care is basically unlimited, we are confident that the study identified virtually all hospitalizations occurring in all patients with MS in France over 11 years (67 million patients registered).”

Disclosures: Multiple study authors declared affiliations with biotech, pharmaceutical and/or device companies. Please see the original reference for a full list of authors’ disclosures.