There is no evidence that vaccinations increase the likelihood of MS.
Researchers at the Technical University of Munich (TUM) in Germany studied data on more than 200,000 people who were representative of the general population.
The data came from the Bavarian Association of Statutory Health Insurance Physicians records covering the period 2005–2017.
The records held people's vaccination history and diagnosed conditions and included data on 12,262 people with a diagnosis of multiple sclerosis (MS).
The dataset included dates of vaccinations for chickenpox, measles, mumps, rubella, influenza, meningococci, pneumococci, human papillomavirus (HPV), tick-borne encephalitis (TBE), and hepatitis A and B.
The researchers used statistical tools to assess any links between MS and vaccinations in the 5 years leading up to diagnosis.
The results did "not reveal vaccination to be a risk factor for MS," the authors conclude in a recent Neurology paper on the study.
An unpredictable autoimmune disease
MS is a long term disease that damages the central nervous system (CNS) by destroying the insulation around nerve fibers.
Experts believe that MS is an autoimmune condition in which the immune system attacks the CNS in the same way as it defends against threats, such as viruses and bacteria.
According to the National Multiple Sclerosis Society, MS affects more than 2.3 million people worldwide.
Estimates suggest that there could be nearly 1 million adults living with MS in the United States.
While it can strike at any age, MS usually develops between the ages of 20 and 50 years. Women are three times more likely to develop MS than men.
The symptoms of MS are unpredictable and vary from person to person, depending on where the damage to the CNS occurs. There can be a pattern of flare-ups that come and go, or the symptoms can worsen with time.
People with MS typically experience fatigue, numbness, disturbed vision, problems with balance and coordination, and speech difficulties. People can also experience problems with memory and concentration. Occasionally, the disease can cause blindness and paralysis.
Findings true for all vaccinations
Senior study author Prof. Bernhard Hemmer, who is the director of the Neurology Department at TUM's hospital Klinikum rechts der Isar, and his colleagues set out to test the hypothesis that vaccination is a risk factor for MS.
They analyzed the data in various ways, using "different time frames, control cohorts, and definitions of the MS cohort."
In analyzing different control cohorts, they compared individuals with MS with those without MS. They also compared those with MS with individuals with two other autoimmune diseases: Crohn's and psoriasis.
The results revealed that in the 5 years before receiving a diagnosis, participants who developed MS had received fewer vaccinations than those who did not develop the condition.
"The odds of MS were lower in participants with a recorded vaccination," write the authors.
Potential immune system reasons
The researchers suggest that one reason for the finding could be that people who develop MS notice their symptoms long before they receive a diagnosis and perhaps avoid vaccinations in order not to stress their immune systems.
"Such effects are, in fact, evident in our data," says lead study author Alexander Hapfelmeier of the Institute of Medical Informatics, Statistics, and Epidemiology at TUM.
Another possible reason behind the findings is that vaccinations somehow prevent the immune system from mounting an attack on the CNS. The authors call for further studies to investigate this effect.
"In any case, given the large volume of data analyzed, we can conclusively state that there is no evidence that recent vaccination increases the likelihood of MS or the onset of an initial MS episode."