Previous research has suggested that certain vaccinations may increase the risk of central nervous system disorders, including multiple sclerosis. But a new study published in JAMA Neurology finds no such association.

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Researchers found no long-term association between vaccinations and central nervous system disorders.

“The concern that vaccinations could induce a small increased risk of multiple sclerosis (MS) and other acquired central nervous system demyelinating syndromes (CNS ADS) remains controversial,” notes the research team, led by Dr. Annette Langer-Gould of Kaiser Permanente in California.

In particular, concerns have been raised about MS risk following vaccinations for hepatitis B, after studies claimed the vaccine could break down myelin (a fatty substance that protects nerve fibers) – a process believed to contribute to MS. Some studies have also suggested a link between the human papillomavirus (HPV) vaccine and increased risk of central nervous system disorders.

However, Dr. Langer-Gould and her team say that such studies have been subject to important limitations, such as a small number of vaccinated cases and incomplete case-finding methods.

In this latest study, the researchers set out to assess the link between vaccinations and MS and other central nervous system disorders in more detail.

To reach their findings, the researchers analyzed health records from members of Kaiser Permanente Southern California (KPSC). They identified 780 patients with central nervous system disorders and 3,885 controls.

Vaccinations the patients received were identified through analysis of electric vaccination records, and the researchers assessed the relationship between vaccinations and subsequent development of MS or central nervous system disorders.

The researchers say that they found no link between any vaccines – including HPV vaccines and hepatitis B vaccines – and an increased risk of MS or any other central nervous system disorder up to 3 years following vaccination.

However, they did find a link between vaccines and increased risk of central nervous system disorders among younger patients in the 30 days after vaccination, but the association disappeared after 30 days. The researchers say this indicates that “at most, vaccines are redundant enhancers of pre-existing autoimmunity.”

Commenting on their findings, the team says:

In this nested case-control study, we found no long-term association between vaccines and MS or other CNS ADS. Our findings do not warrant any change in vaccine policy.”

The team notes, however, that the link between HPV vaccines and increased risk of central nervous system disorders is “inconclusive” because of the small number of cases included; only 92 female study participants aged 9-26 received the HPV vaccine.

Other limitations of the study include the small number of older patients included and the inability to assess subgroups at high risk of MS – such as those with a family history of the disease. They note they were also unable to determine how preservatives present in vaccines influenced the risk of central nervous system disorders.

Medical News Today recently reported on a study published in The BMJ claiming that people infected with HIV are at much lower risk of MS than those without the infection.