Post-marketing monitoring of intussusception after rotavirus vaccination in Japan

PurposeRotarix(TM) was launched in November 2011 in Japan to prevent rotavirus gastroenteritis. Some studies suggest that Rotarix(TM) may have a temporal association with a risk of intussusception (IS). We assessed a possible association between IS and Rotarix(TM) vaccination in Japan. MethodsAll IS cases spontaneously reported post-vaccination (Brighton collaboration levels 1, 2, and 3) were extracted from the GlaxoSmithKline spontaneous report database on the 11th of January 2013. Expected numbers of IS cases were estimated using the number of vaccine doses distributed and the Japanese incidence rate of IS stratified by month of age. The observed versus expected analysis considered the IS cases for each risk period (7 and 30days post-vaccination) and for each vaccine dose (two doses). ResultsBefore January 2013, approximately 601000 Rotarix(TM) doses were distributed in Japan. For a risk period of 7days post-dose 1 and post-dose 2, 10 and five IS cases were observed, whereas 3.4 and 7.6 were expected, providing an observed-to-expected ratio of 2.96 (95% confidence interval [CI]: 1.42; 5.45) and 0.66 (95% CI: 0.21; 1.53), respectively. For a risk period of 30days post-dose 1 and post-dose 2, 14 and eight cases were observed, whereas 14.5 and 32.7 were expected, providing an observed-to-expected ratio of 0.97 (95% CI: 0.53; 1.62) and 0.24 (95% CI: 0.11; 0.48), respectively. ConclusionA statistically significant excess of IS cases was observed within 7days post-dose 1, but not post-dose 2. These results are consistent with previous observations in large post-marketing safety studies in other world regions. (c) 2015 The Authors. Pharmacoepidemiology and Drug Safety published by John Wiley & Sons, Ltd.