The Japanese Experience with Vaccinating Schoolchildren against Influenza

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Abstract

Influenza epidemics lead to increased mortality, principally among elderly persons and others at high risk, and in most developed countries, influenza-control efforts focus on the vaccination of this group. Japan, however, once based its policy for the control of influenza on the vaccination of schoolchildren. From 1962 to 1987, most Japanese schoolchildren were vaccinated against influenza. For more than a decade, vaccination was mandatory, but the laws were relaxed in 1987 and repealed in 1994; subsequently, vaccination rates dropped to low levels. When most schoolchildren were vaccinated, it is possible that herd immunity against influenza was achieved in Japan. If this was the case, both the incidence of influenza and mortality attributed to influenza should have been reduced among older persons. We analyzed the monthly rates of death from all causes and death attributed 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 November. The excess mortality from pneumonia and influenza and that from all causes were highly correlated in each country. In the United States, these rates were nearly constant over time. With the initiation of the vaccination program for schoolchildren in Japan, excess mortality rates dropped from values three to four times those in the United States to values similar to those in the United States. The vaccination of Japanese children prevented about 37,000 to 49,000 deaths per year, or about 1 death for every 420 children vaccinated. As the vaccination of schoolchildren was discontinued, the excess mortality rates in Japan increased. 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 of deaths from all causes and deaths attributed to pneumonia or influenza. Vaccinating schoolchildren against influenza provides protection and reduces mortality from influenza among older persons.

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Most cited references 31

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The effect of influenza on hospitalizations, outpatient visits, and courses of antibiotics in children.

K Neuzil, B Mellen, P. Wright … (2000)

Despite high annual rates of influenza in children, influenza vaccines are given to children infrequently. We measured the disease burden of influenza in a large cohort of healthy children in the Tennessee Medicaid program who were younger than 15 years of age. We determined the rates of hospitalization for acute cardiopulmonary conditions, outpatient visits, and courses of antibiotics over a period of 19 consecutive years. Using the differences in the rates of these events when influenzavirus was circulating and the rates from November through April when there was no influenza in the community, we calculated morbidity attributable to influenza. There was a total of 2,035,143 person-years of observation. During periods when influenzavirus was circulating, the average number of hospitalizations for cardiopulmonary conditions in excess of the expected number was 104 per 10,000 children per year for children younger than 6 months of age, 50 per 10,000 per year for those 6 months to less than 12 months, 19 per 10,000 per year for those 1 year to less than 3 years, 9 per 10,000 per year for those 3 years to less than 5 years, and 4 per 10,000 per year for those 5 years to less than 15 years. For every 100 children, an annual average of 6 to 15 outpatient visits and 3 to 9 courses of antibiotics were attributable to influenza. In winter, 10 to 30 percent of the excess number of courses of antibiotics occurred during periods when influenzavirus was circulating. Healthy children younger than one year of age are hospitalized for illness attributable to influenza at rates similar to those for adults at high risk for influenza. The rate of hospitalization decreases markedly with age. Influenza accounts for a substantial number of outpatient visits and courses of antibiotics in children of all ages.

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Hector Izurieta, William W Thompson, Piotr Kramarz … (2000)

Young children may be at increased risk for serious complications from influenzavirus infection. However, in population-based studies it has been difficult to separate the effects of influenzavirus from those of respiratory syncytial virus. Respiratory syncytial virus often circulates with influenzaviruses and is the most frequent cause of hospitalization for lower respiratory tract infections in infants and young children. We studied the rates of hospitalization for acute respiratory-disease among infants and children during periods when the circulation of influenzaviruses predominated over the circulation of respiratory syncytial virus. For each season from October to May during the period from 1992 to 1997, we used local viral surveillance data to define periods in Washington State and northern California when the circulation of influenzaviruses predominated over that of respiratory syncytial virus. We calculated the rates of hospitalization for acute respiratory disease, excess rates attributable to influenzavirus, and incidence-rate ratios for all infants and children younger than 18 years of age who were enrolled in either the Kaiser Permanente Medical Care Program of Northern California or the Group Health Cooperative of Puget Sound. The rates of hospitalization for acute respiratory disease among children who did not have conditions that put them at high risk for complications of influenza (e.g., asthma, cardiovascular diseases, or premature birth) and who were younger than two years of age were 231 per 100,000 person-months at Northern California Kaiser sites (from 1993 to 1997) and 193 per 100,000 person-months at Group Health Cooperative sites (from 1992 to 1997). These rates were approximately 12 times as high as the rates among children without high-risk conditions who were 5 to 17 years of age (19 per 100,000 person-months at Northern California Kaiser sites and 16 per 100,000 person-months at Group Health Cooperative sites) and approached the rates among children with chronic health conditions who were 5 to 17 years of age (386 per 100,000 person-months and 216 per 100,000 person-months, respectively). Infants and young children without chronic or serious medical conditions are at increased risk for hospitalization during influenza seasons. Routine influenza vaccination should be considered in these children.

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The impact of influenza epidemics on mortality: introducing a severity index.

L Simonsen, M J Clarke, G D Williamson … (1997)

The purpose of this study was to assess the impact of recent influenza epidemics on mortality in the United States and to develop an index for comparing the severity of individual epidemics. A cyclical regression model was applied to weekly national vital statistics from 1972 through 1992 to estimate excesses in pneumonia and influenza mortality and all-cause mortality for each influenza season. Each season was categorized on the basis of increments of 2000 pneumonia and influenza excess deaths, and each of these severity categories was correlated with a range of all-cause excess mortality. Each of the 20 influenza seasons studied was associated with an average of 5600 pneumonia and influenza excess deaths (range, 0-11,800) and 21,300 all-cause excess deaths (range, 0-47,200). Most influenza A(H3N2) seasons fell into severity categories 4 to 6 (23,000-45,000 all-cause excess deaths), whereas most A(H1N1) and B seasons were ranked in categories 1 to 3 (0-23,000 such deaths). From 1972 through 1992, influenza epidemics accounted for a total of 426,000 deaths in the United States, many times more than those associated with recent pandemics. The influenza epidemic severity index was useful for categorizing severity and provided improved seasonal estimates of the total number of influenza-related deaths.