Invasive Haemophilus influenzae infections in children in Kamikawa subprefecture, Hokkaido, Japan, 2006-2015: The effectiveness of H. influenzae type b vaccine.

We evaluated 24 children with invasive Haemophilus influenzae infections between 2006 and 2015 in Kamikawa subprefecture of Hokkaido, Japan. The most frequent disease was pneumonia in 12 cases (50.0%), followed by meningitis in 7 (29.2%) and bacteremia in 5 (20.8%). Patients ranged in age from 3 months to 12 years of age. Seventeen (70.8%) of the total were less than 2 years old. The incidence rate of H. influenzae infection varied from 15.1 to 36.3 per 100,000 population in the Kamikawa area during the period from 2006 through 2011. The corresponding rate decreased to 10.4 per 100,000 population in 2012, and there were no cases after 2013. Meningitis occurred in 1-2 patients annually from 2006 to 2011, showing an incidence rate of 4-10 per 100,000 population per year, while no cases were reported during or after 2012. No patients with invasive H. influenzae infection died, but sequelae were seen at discharge in 1 patient with meningitis, that had hydrocephalus and developmental delay. In Japan, introduction of the H. influenzae type b (Hib) vaccine was in November 2008. Initially, this vaccination was voluntary, resulting in a low vaccination rate. According to the national policy, and the self-pay burden for vaccination was decreased in December 2010, and the vaccination rate increased markedly to over 90%. This report provides a meaningful demonstration that introduction of the Hib vaccine markedly reduced invasive H. influenzae infections, exerting a beneficial effect in Japan, as it has in the world.