(MS), according to an analysis published July 30 in Neurology. Although the results suggest that vaccination is associated with a lower likelihood of incident MS within the following 5 years, “these data alone do not allow for any conclusion regarding a possible protective effect of vaccinations regarding the development of MS,” wrote Alexander Hapfelmeier, PhD, of the Technical University of Munich and colleagues.
Technical University of Munich
Dr. Alexander Hapfelmeier (left) and Dr. Bernhard Hemmer
In recent years, researchers have proposed and investigated various potential environmental risk factors for the development of MS. Vaccination is one proposed environmental risk factor, but case reports and small studies have yielded conflicting results about its association with incident MS.
To examine this question more closely, Dr. Hapfelmeier and colleagues performed a systematic retrospective analysis of ambulatory claims data held by the Bavarian Association of Statutory Health Insurance Physicians. They reviewed the data to identify patients with new-onset MS and at least two ICD-10 diagnoses of the disorder. They next identified two control cohorts of participants diagnosed with other autoimmune diseases: Crohn’s disease and psoriasis. Finally, they randomly selected a third control cohort of patients without any of these diagnoses and matched them by age, sex, and district to patients with MS in a 5:1 ratio. Eligible participants were younger than 70 years.
Dr. Hapfelmeier and colleagues reviewed the incidence and frequency of vaccinations (such as those targeting tick-borne encephalitis, human papillomavirus, and influenza virus) in all cohorts. They created unconditional logistic regression models to assess the association between vaccination and MS. They also created separate models to contrast the MS cohort with each of the control cohorts.
The researchers included 12,262 patients with MS, 19,296 patients with Crohn’s disease, 112,292 patients with psoriasis, and 79,185 participants without these autoimmune diseases in their analysis. They found 456 participants with Crohn’s disease and psoriasis, 216 participants with MS and psoriasis, 48 participants with Crohn’s disease and MS, and 2 participants with Crohn’s disease, psoriasis, and MS. Dr. Hapfelmeier and colleagues allocated these participants to each of the respective cohorts and did not analyze them differently because of the comparatively small sample sizes.
The investigators analyzed the occurrence of vaccination in all participants during the 5 years before first diagnosis. Among patients who received vaccination, the odds ratio of MS was 0.870 in participants without autoimmune disease, 0.919 in participants with Crohn’s disease, and 0.973 in participants with psoriasis. Decreased risk of MS was most notable for vaccinations against influenza and tick-borne encephalitis. The results were consistent regardless of time frame, control cohort, and definition of MS.
The subjective definition of the MS cohort was a limitation of the study, but the authors addressed it by also using several strict definitions of that cohort. Another limitation is that the source data may reflect entry errors and incorrect coding.
A grant from the German Federal Ministry of Education and Research Competence Network MS supported the study. The authors had no conflicts that were relevant to the topic of the study.
SOURCE: Hapfelmeier A et al. Neurology. 2019 Jul 30. doi: 10.1212/WNL.0000000000008012.