Relapse risk in patients with multiple sclerosis after H1N1 vaccination, with or without seasonal influenza vaccination

Abstract

The safety of vaccination in multiple sclerosis (MS) raises concern, particularly the relapse risk post-vaccination. With the recent H1N1 pandemic, people with chronic diseases, including neurological conditions such as MS, were prioritised for vaccination. Two questions therefore arise in this context: whether vaccination increases the relapse rate, and whether the relapse is more severe postvaccination. Seasonal influenza immunisation does not increase the risk of MS exacerbation; a systematic review found no increased risk of early (3–4 weeks post-vaccination) or late (4–6 months) exacerbations [1]. Likewise, influenza vaccination resulted in no relative increase in disease-activity to controls based on new Gd-enhancing lesions on MRI [2, 3]. The evidence is less clear-cut regarding the pandemic influenza H1N1 vaccine and relapse risk. Reports from the 1970s suggested an increased risk of Guillan-Barre and MS-like syndromes following this vaccine [4], although formal controlled trials did not. Two placebo controlled studies involving 88 and 127 MS patients, reported similar frequency of MS relapses in the H1N1 and placebo-vaccinated groups [5, 6] (12 vs. 14% and 3 vs. 6.5%, respectively). In our acute weekly relapse clinic, we recorded data from 30 consecutive patients between 11/2009 and 01/2010. During this period in the UK, all MS patients were actively offered H1N1 vaccination [7]. Relapse onset date, and H1N1/seasonal influenza vaccination status (with administration date where appropriate) were recorded. The expanded disability status scale (EDSS), multiple sclerosis impact scale (MSIS-29 v 2.0), and use of corticosteroid treatment were also documented. Eighteen (60%) of patients received either/both vaccination prior to relapse onset, leaving 40% not vaccinated (Table 1). Neither the relapse severity (EDSS/MSIS-29 v 2.0) nor the numbers receiving corticosteroid treatment were significantly different (Table 1). The association between relapse rate and vaccination in a relapse clinic can be evaluated using a case-crossover design; as in a previous report of different vaccinations in MS relapse clinics [8]. This method compares vaccine exposure in a specified risk period immediately preceding the relapse to that in several prior control periods of equal duration, thus quantifying the relative relapse risk in the specified post-vaccination period. Using a similar analysis in our 30 patients, 15 received H1N1 vaccination (Fig. 1a, flow chart); of whom 10