The Japanese experience with vaccinating schoolchildren against influenza.

Background: Influenza epidemics lead to increased mortality, principally am ong elderly persons and others at high risk, and in most developed countrie s, influenza-control efforts focus on the vaccination of this group. Japan, however, once based its policy for the control of influenza on the vaccina tion of schoolchildren. From 1962 to 1987, most Japanese schoolchildren wer e vaccinated against influenza. For more than a decade, vaccination was man datory, but the laws were relaxed in 1987 and repealed in 1994; subsequentl y, vaccination rates dropped to low levels. When most schoolchildren were v accinated, it is possible that herd immunity against influenza was achieved in Japan. If this was the case, both the incidence of influenza and mortal ity attributed to influenza should have been reduced among older persons. Methods: We analyzed the monthly rates of death from all causes and death a ttributed to pneumonia and influenza, as well as census data and statistics on the rates of vaccination for both Japan and the United States from 1949 through 1998. For each winter, we estimated the number of deaths per month in excess of a base-line level, defined as the average death rate in Novem ber. Results: The excess mortality from pneumonia and influenza and that from al l causes were highly correlated in each country. In the United States, thes e rates were nearly constant over time. With the initiation of the vaccinat ion program for schoolchildren in Japan, excess mortality rates dropped fro m values three to four times those in the United States to values similar t o those in the United States. The vaccination of Japanese children prevente d about 37,000 to 49,000 deaths per year, or about 1 death for every 420 ch ildren vaccinated. As the vaccination of schoolchildren was discontinued, t he excess mortality rates in Japan increased. Conclusions: The effect of influenza on mortality is much greater in Japan than in the United States and can be measured about equally well in terms o f deaths from all causes and deaths attributed to pneumonia or influenza. V accinating schoolchildren against influenza provides protection and reduces mortality from influenza among older persons. (N Engl J Med 2001;344:889-9 6.) Copyright (C) 2001 Massachusetts Medical Society.