Factors involved in immunization program for swine influenza.

The decision to undertake a nationwide program of vaccination against swine influenza requires assessment of the status of immunity of those in various age groups in our population against this agent. Pools of serum were collected from persons born in the years from 1889 to 1943; they were tested for hemaggultinin inhibiting (HI) antibody against the HSW 1N1 influenza virus strains isolated in 1931 and 1976. The titers secured serve as an indication of the average level of immunity of those of different ages. Persons less than 43 years of age are found to be without antibody protection. The need for vaccination of people in different age groups based on mortality statistics of previous epidemics is evaluated. It is realized that no epidemic may occur and that a reduced virulence of the viral agent and use of antibiotics may reduce the death rate if the infection recurs. The extraordinary high mortality in 1918 in people between 15 and 44 years of age deserves recognition together with the fact that those in the same age group are now without protection. The fact that women of childbearing age fall into this group deserves special consideration in view of increased mortality in puerperal women observed in the pandemics of 1918 and 1957. The degree of protection afforded the newborn by transplacental transmission of maternal antibodies is discussed. The need of increasing the level of immunity in those who have varying titers of HI antibodies is considered in relation to the prevalence of cardiopulmonary complications and other chronic diseases in older subjects.