By Eleanor McDermid, Senior medwireNews Reporter
A study of almost 4 million girls and women allays fears that receipt of the quadrivalent human papillomavirus (HPV) vaccine could increase the risk of developing multiple sclerosis, or other demyelinating disorders.
Indeed, the findings published in JAMA show that the crude rate of these conditions was somewhat lower within 2 years after vaccination than at other times, simply because at the time of vaccination the study participants were below the peak age for diagnosis of these conditions.
The crude incidence rate of multiple sclerosis within 2 years of vaccination was 6.12 per 100,000 person–years among 788,986 vaccinated girls and women, aged 10 to 44 years, whose details were obtained from national registries in Sweden and Denmark.
Among the 3,978,271 participants overall, the multiple sclerosis incidence was 21.54 per 100,000 person–years during unvaccinated periods, comprising the entire follow-up for unvaccinated women and periods excluding the 2 years after vaccination for vaccinated women. This gave a nonsignificant risk ratio of 0.90 after accounting for confounders including age.
The findings were similar for other demyelinating diseases, with incidences of 7.54 and 16.14 per 100,000 person–years during vaccinated and unvaccinated periods, respectively, and an adjusted risk ratio of 1.00.
A total of 4322 cases of multiple sclerosis occurred, including 339 among vaccinated patients, but these were no more likely to occur within 2 years of vaccination than at any other time (incidence ratio=1.05, nonsignificant), and the same was true for the 3300 cases of other demyelinating diseases (incidence ratio=1.14, nonsignificant).
Vaccination was also not related to multiple sclerosis risk when examining specific risk windows, extending to more than 2 years after vaccination, or when stratifying by age or country, report Nikolai Madrid Scheller (Statens Serum Institut, Copenhagen, Denmark) and study co-authors.
They say: “Given the upper limits of the confidence intervals, the study can exclude a potential 16% increased risk of multiple sclerosis and a 27% increased risk of other central demyelinating diseases.”
Concerns about an increased risk of such conditions came from case reports in social and news media, and in the medical literature, of cases occurring after HPV vaccination, say the researchers, with cases including multiple sclerosis, optic neuritis, transverse myelitis, acute disseminated encephalomyelitis and neuromyelitis optica.
But the team concludes that their findings “do not support concerns about a causal relationship between [quadrivalent] HPV vaccination and demyelinating diseases.”
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