RECURRENT ASIAN INFLUENZA IN AN INDUSTRIAL POPULATION

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Abstract
Two epidemics of Asian influenza occurred in personnel of a large oil refinery and petrochemical plant. Monthly attack rates and sickness absenteeism data demonstrated the epidemiologic pattern of the disease: its abrupt appearance in September, 1957 and persistence into the Spring of 1958, followed by apparent disappearance in the worker population until it recurred in February, 1960, as a sharp, explosive outbreak. The clinical and epidemiologic findings were corroborated by virologic and serologic studies during the three year period. Vaccination in 1957-1958 and in October, 1959 provided significant levels of protection for inoculated workers during the epidemics. Reduction in cases of clinically recognized influenza in vaccinated employees was 60% in 1957-1958 and 20% in 1960; corresponding reductions in absenteeism were 65% in 1957-1958, and 27% in 1960. Factors of vaccine dosage and schedule which might bring about differences in protection are discussed. Either individual or pooled serum samplings obtained from the population under observation could be used to determine the virus experience during the previous year or to predict the susceptibility of the group in the approaching season. Six hundred workers with typical influenza in 1960 were matched with 600 workers free of respiratory diseases during the 1960 epidemic period. Only the most recent (October 1959) vaccination was shown to be effective in preventing influenza in 1960. Other factors, including previous immunizations or disease experience, had no influence upon occurrence of the disease in the 1960 epidemic.

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