An evaluation of pertussis vaccine.

Infant mortality from pertussis in the United States was 4.5 deaths/1,000 in 1900 but decreased to 0.003 deaths/1,000 by 1974. The attribution of this decrease in mortality to the widespread use of pertussis vaccine, which began in the 1940s, has been questioned because death rates from pertussis in infants steadily declined by 70% between 1900-1904 and 1935-1939. Thes doubts are compounded by the uncertain frequency and significance of untoward reactions to the vaccine. An attempt was made to clarify this issue by statistical analysis. Because most deaths from pertussis occur in the young, death rates were determined for consecutive five-year periods from 1900 through 1974 among children younger than one year of age (infants) and among those from one to four years of age. there was an accelerated decline in mortality beginning in 1940, especially among infants (P < 0.01 vs. mortality in 1930-1939). On the basis of the rate of decline before 1940, 4,000-8,000 deaths from pertussis would be expected to hve occurred in 1970-1974; however, only 52 such deaths occurred. It is unlikely that factors other than pertussis vaccine caused this decline in mortality. Therefore, the vaccine's benefit-risk ratio probably is high.