Influenza pandemics: lessons for the future

• Published in: Vaccine 2002-05, Vol.20 Suppl 2, p.S15-S15
• Main Author: Dowdle, Walter R
• Format: Article
• Language: English
• Subjects: Humans; Influenza A virus - classification; Influenza, Human - prevention & control; Influenza, Human - virology
• ISSN: 0264-410X
• DOI: 10.1016/S0264-410X(02)00122-6

This report critically reviews the data on which the concept of influenza A virus recycling is based and discusses the implications for pandemic planning. Pandemics that occurred prior to the isolation of the first influenza virus type A from humans in 1933, were linked to subtypes based on retrospective studies of sera from the elderly or "seroarcheology". For nearly 30 years, textbooks and reviews have stated that H2 first appeared about 1889, H3 about 1900, H1 in 1918, H2 in 1957 and H3 in 1968. A review of the data does not support this pattern. Recent findings of swine influenza virus HA genes in persons who died of influenza during the pandemic of 1918-1920, validate the H1 seroarcheological pattern as a model for other pandemic periods. Application of the model to seroprevalence curves constructed from hemagglutination-inhibition (HI) test results on sera collected before 1968 link the pandemic of 1889-1891 to an H3-like virus, not H2 as popularly quoted. Additional evidence linking an H3-like virus with the 1889-1891 pandemic is the sharp decrease in expected excess mortality during the H3 pandemic of 1968-1969 among persons born prior to 1893. No similar body of data provides consistent evidence for pre-existing H2 antibody in the elderly. The origin of H2 antibodies of low prevalence among persons born in the late 1800s is uncertain. However, it is certain that in the last half of the 19th century an H2-like virus, if it occurred at all, was not associated with an influenza event comparable to that of H3 in 1889-1891 or H1 in 1918-1920. Evidence suggests that H3 circulated twice in the past 200 years, from 1889 to 1891 to some undetermined time prior to 1918 and from 1968 to the present. H2 circulated once in the past 130 years, from 1957 to 1967. H1 circulated twice in the past 170 years, from 1918 to 1956 and from 1977 to the present, although the origin of the 1977 H1 virus may not have been a natural event. Pandemics have occurred in unpredictable patterns of time and etiology and do no predict future events. Further, the world has changed over the past 300 years and so likely has the epidemiology of influenza. An influenza pandemic may occur tomorrow or not within our lifetime, we cannot be certain. The key to influenza preparedness is effective global surveillance.