Mandatory Vaccination of Japanese Schoolchildren Demonstrates "Herd Immunity".(Brief Article)

2001 APR 11 - (NewsRx.com & NewsRx.net) --

by N.R. Saltmarsh, staff medical writer - During a 25-year period when most Japanese children were immunized against influenza, fewer elderly people died from the disease.

That lower mortality rate was likely due to a "herd immunity" generated by the mass vaccination of schoolchildren, according to a report in the New England Journal of Medicine.

Thomas A. Reichert and colleagues reviewed nearly half a century of data from before, during, and after the 1962-1987 period when most students received the vaccine. In 1987 Japan relaxed the vaccination mandate that had been in place for more than a decade, and after it was repealed in 1994, vaccination rates among children were low.

"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," reported Reichert et al. "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 researchers found that in the United States, which did not require or encourage vaccination of schoolchildren for influenza, excess mortality in the elderly from the virus as well as that from pneumonia and all causes remained constant. In Japan, it was three to four times higher before mass vaccination of schoolchildren, but dropped to levels similar to the U.S. during the vaccination period. The rate climbed again when children stopped being routinely vaccinated.

The mass vaccination of Japanese children prevented ...