Effect of mass immunization against influenza encephalopathy on mortality rates in children.
BACKGROUND
Since the Japanese influenza vaccination program for school children was terminated in 1994, a steep rise has been noted in the number of young children reported with fulminant influenza and influenza associated with acute encephalopathy/encephalitis. The purpose of the present study was to interpret and clarify the effect of mass influenza vaccination on mortality of Japanese children, aged <19 years, with influenza and influenza-associated acute encephalopathy/encephalitis.


METHODS
The authors examined the distribution of mortality rates of children in Japan aged <19 years with influenza during 1950-2000, influenza associated with central nervous system (CNS) signs in the period 1950-1978, and the estimated cases of influenza associated with acute encephalopathy/encephalitis in the period 1987-2000.


RESULTS
Total influenza mortality among children aged <19 years has increased since 1990, with children aged <4 years after 1994 being the worst affected. The mean values of mortality rates of influenza associated with central nervous system signs during 1963-1978 and the estimated mortality of children aged <9 years during 1979-1994 were significantly lower than in some years before 1962, and after 1995 (P < 0.05). The annual mortality rates of influenza-associated acute encephalopathy/encephalitis during 1995-2000 were significantly higher than the expected mortality of influenza associated with central nervous system signs in children aged <14 years (P < 0.05).


CONCLUSIONS
The results of the present study suggest that mass immunization of school-aged children reduced the mortality rate from influenza-associated acute encephalopathy/encephalitis in children less than 9 years of age.
Ono
Shigetoo
S
Division of Preventive Medicine Department of Human Environmental and Social Medicine, Faculty of Medicine, Oita University, Hasama, Oita, Japan.
Kudo
Masanobu
M
Aoki
Kazuo
K
Ezaki
Fusako
F
Misumi
Junichi
J
D000208:Acute Disease; D000293:Adolescent; D001927:Brain Diseases / Q000401:mortality* / Q000821:virology; D002648:Child; D002675:Child, Preschool; D018792:Encephalitis, Viral / Q000401:mortality* / Q000821:virology; D006801:Humans; D017589:Immunization Programs; D007223:Infant; D007251:Influenza, Human / Q000401:mortality* / Q000517:prevention & control*; D007564:Japan / Q000453:epidemiology; D037141:Mandatory Programs; D015996:Survival Rate