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 inter season deaths in the elderly can
be prevented by vaccinating schoolchildren against influenza, according to a
recent study. Historically, Japan is the only country that has ever based its
influenza control policy on the vaccination of schoolchildren rather than
elderly persons. Special programs of vaccination against influenza for
schoolchildren were initiated in 1962, and legislation enacted in 1977 made
influenza vaccination obligatory for this group. In 1987, however, new
legislation permitted parents to refuse influenza vaccination of their
children, and in 1994, the program of immunizing schoolchildren against
influenza was discontinued.
Recently, a team of experts in influenza
epidemiology, mortality and morbidity, and vaccine usage from Japan and the
United States analyzed data on all-cause mortality and that attributed to
pneumonia and influenza in the two countries, as well as census data and
statistics on the rates of vaccination, for 1949 through 1998 (N Engl J
Med. 2001;344:889-896). The study was undertaken to determine whether a
reduction in excess mortality occurred during winter influenza seasons in
Japan during the years in which high rates of influenza vaccination were
reported in schoolchildren.
The excess mortality from pneumonia and
influenza, as well as mortality from all causes, was highly correlated and
similarly proportional in each country, according to principal investigator
Thomas A. Reichert, PhD, MD, formerly of Becton Dickinson and now at the
consulting firm of Entropy Limited in Lincoln, Massachusetts. Whereas in the
United States these rates were nearly constant over time, excess mortality
rates in Japan dropped from values three to four times those in the United
States to values similar to those in the United States when influenza
vaccination in schoolchildren was implemented. The vaccination of Japanese
schoolchildren prevented an estimated 37,000 to 49,000 deaths per year—about
one death for every 420 schoolchildren vaccinated. This became clear only
when the vaccination of schoolchildren was discontinued and the excess
mortality rates in Japan rose. Whereas the number of excess deaths during the
winter season in Japan declined from 1962 until 1987, in spite of a large
increase in the number of elderly persons, the number of excess deaths began
to climb after 1987, and the increase became quite rapid after 1994.
“The most likely explanation for this changing
pattern of seasonal mortality is that the herd immunity produced by mass
immunization of schoolchildren protected elderly persons,” the investigators
wrote. Other factors considered include improvements in the social
infrastructure and health care as well as technological advances and changes
in social custom, which occurred during the period when excess mortality
declined and then began to rise.
In preschool children, live attenuated
influenza vaccine has been shown to provide about 90% protection against
influenza-induced illness (N Engl J Med. 1998;338:1405-1412; J
Pediatr. 2000;136:168-175), and modeling studies suggest that
administering influenza vaccine to 70% of preschool and school-aged children
would be highly likely to prevent communitywide epidemics (Vaccine.
2000;18:1902-1909). Other studies have indicated that influenza vaccine could
be cost-effective in school-aged children in the United States (Pediatrics.
1999;103:1273. Abstract).
Large, long-term trials are under way in Texas
to determine whether vaccinating 85% of schoolchildren and 50% of preschool
children who are 18 months of age or older with a cold-adapted, live
attenuated vaccine can control the spread of influenza. According to Paul
Glezen, MD, of Baylor College of Medicine in Houston, about 9500 children
have received the influenza vaccine, and safety data are good.
According to Dr. Reichert and associates, the
findings of their study, together with the results of ongoing studies,
warrant a reconsideration of current recommendations for the use of
inactivated and live attenuated influenza vaccines, to encourage use of these
vaccines in infants, children, and adults. Specific consideration of the
vaccination of schoolchildren in pandemic planning is also warranted.
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When the program of immunizing Japanese schoolchildren was discontinued in
1994, excess mortality rates rose rapidly.
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