Influenza and risk of later celiac disease: a cohort study of 2.6 million people

<p><b>Objectives:</b> Influenza has been linked to autoimmune conditions, but its relationship to subsequent celiac disease (CD) is unknown. Our primary aim was to determine the risk of CD after influenza. A secondary analysis examined the risk of CD following pandemic influenza vaccination.</p> <p><b>Methods:</b> This nationwide register-based cohort study included 2,637,746 Norwegians (born between 1967–2013) followed during 2006–2014 with information on influenza diagnosed in primary or non-primary care, pandemic vaccination (Pandemrix), and subsequent CD. Cox regression yielded hazard ratios adjusted (HR) for socio-demographic characteristics and earlier healthcare use.</p> <p><b>Results:</b> During 13,011,323 person-years of follow-up 7321 individuals were diagnosed with CD (56/100,000 person-years). There were 351,666 individuals diagnosed with influenza, including 82,980 during the 2009–2010 pandemic, and 969,968 individuals were vaccinated. Compared with participants without influenza, who had a CD incidence of 55/100,000 person-years, those diagnosed with seasonal and pandemic influenza had a rate of 68 and 78, per 100,000 person-years, respectively. The HR for CD was 1.29 (95%CI, 1.21–1.38) after seasonal influenza and 1.29 (95%CI, 1.15–1.44) after pandemic influenza; HRs remained significantly increased one year after exposure, when restricted to laboratory-confirmed influenza, and after multivariate adjustments. The reverse association, i.e., risk of influenza after CD, was not significant (HR 1.05; 95%CI, 0.98–1.12). The HR for CD after pandemic vaccination was 1.08 (95%CI, 1.03–1.14).</p> <p><b>Conclusion:</b> A positive association with influenza diagnosis is consistent with the hypothesis that infections may play a role in CD development. We could neither confirm a causal association with pandemic vaccination, nor refute entirely a small excess risk.</p>