Hospitalization following influenza infection and pandemic vaccination in multiple sclerosis patients: a nationwide population-based registry study from Norway

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Eur J Epidemiol. 2019 Dec 23. doi: 10.1007/s10654-019-00595-2. [Epub ahead of print] Hospitalization following influenza infection and pandemic vaccination in multiple sclerosis patients: a nationwide population-based registry study from Norway.

Ghaderi S¹, Berg-Hansen P^2,3, Bakken IJ⁴, Magnus P⁴, Trogstad L⁵, H?berg SE⁴.
Author information

1 Department of Global Health and Primary Care, University of Bergen, Post Box 7804, 5020, Bergen, Norway. Sara.Ghaderi@uib.no. 2 Institute of Clinical Medicine, University of Oslo, Oslo, Norway. 3 Department of Neurology, Oslo University Hospital, Oslo, Norway. 4 Centre for Fertility and Health, Norwegian Institute of Health, Oslo, Norway. 5 Department of Infectious Disease Epidemiology and Modelling, Norwegian Institute of Health, Oslo, Norway.

Abstract

Patients with multiple sclerosis (MS) are at increased risk of infections and related worsening of neurological function. Influenza infection has been associated with increased risk of various neurological complications. We conducted a population-based registry study to investigate the risk of acute hospitalization of MS patients in relation to influenza infection or pandemic vaccination in Norway. The entire Norwegian population in the years 2008-2014 was defined as our study population (N = 5,219,296). Information on MS diagnosis, influenza infection and vaccination were provided by Norwegian national registries. The self-controlled case series method was used to estimate incidence rate ratios (IRRs) with 95% confidence intervals (95% CI) in defined risk periods. 6755 MS patients were identified during the study period. Average age at first registration of an MS diagnosis was 51.8 years among men and 49.9 years among females (66.9%). The IRR for emergency hospitalization among MS patients the first week after an influenza diagnosis was 3.4 (95% CI 2.4-4.8). The IRR was 5.6 (95% CI 2.7-11.3) after pandemic influenza, and 4.8 (95% CI 3.1-7.4) after seasonal influenza. Pandemic vaccination did not influence risk of hospitalization [IRR within the first week: 0.7 (95% CI 0.5-1.0)]. Among MS patients, influenza infection was associated with increased risk for acute hospitalization while no increased risk was observed after pandemic vaccination. Influenza vaccination could prevent worsening of MS-related symptoms as well as risk of hospitalization.


KEYWORDS:

Hospitalization; Influenza; Multiple sclerosis; Norway; Pandemic; Pandemrix vaccination

PMID: 31873811 DOI: 10.1007/s10654-019-00595-2