Mass vaccination of schoolchildren against influenza and its impact on the influenza-associated mortality rate among children in Japan.
BACKGROUND
Influenza control based on mass vaccination of schoolchildren was implemented in Japan in the 1960s and was associated with a decrease in the overall mortality rate. The program was discontinued in 1994. The discontinuation was followed by a seasonal increase in the mortality rate. Lately, young children and elderly persons have been receiving influenza vaccines. The purpose of this study was to investigate changes in influenza-related mortality among young children before and after discontinuation of mass vaccination of schoolchildren.


METHODS
We calculated the monthly all-cause mortality rates during 1972-2003 and the pneumonia and influenza (P&I) mortality rates during 1972-1999 for young children (age, 1-4 years). We estimated the excess mortality rates attributable to influenza by computing the baseline annual mortality rate as a centered, 3-year moving average of the number of deaths reported during the 2 preceding and the following Decembers.


RESULTS
Prominent winter peaks in monthly all-cause mortality rates among young children occurred in the 1990s. They coincided with the winter peaks in monthly P&I mortality rates among young children and were very similar to the winter peaks observed among elderly persons. The number of excess deaths of young children was estimated to be 783 in the 11 winter seasons from 1990 to 2000, whereas no winter peaks in the number of deaths were seen after 2000.


CONCLUSIONS
It is likely that discontinuation of mass vaccination of schoolchildren was responsible for the increase in influenza-associated deaths among young children in the 1990s. The recent increase in influenza vaccinations among young children, together with the routine therapeutic use of neuraminidase inhibitors, has led to a decrease in the influenza-associated mortality rate.
Sugaya
Norio
N
Department of Pediatrics, Keiyu Hospital, Yokohama, Kanagawa, Japan. sugaya-n@za2.so-net.ne.jp
Takeuchi
Yoshinao
Y
D000368:Aged; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007223:Infant; D007252:Influenza Vaccines / Q000008:administration & dosage*; D007251:Influenza, Human / Q000453:epidemiology / Q000401:mortality* / Q000517:prevention & control*; D007564:Japan; D032541:Mass Vaccination / Q000379:methods*; D012189:Retrospective Studies; D013997:Time Factors
D007252:Influenza Vaccines