Background: Influenza pandemics in this century (1946-1947, 1957 and 1968) have fascinated some people for the idea of 11-year pattern pandemic cycles. In solar physics, it is well known that sunspot cycles also have regular periods of around 11 years. This study therefore aims to investigate the association between sunspot cycles and the occurrences of pandemic influenza. The hypothesis here states that sunspot numbers can detect pandemic influenza A between 1700 and 2000 A.D.
Presentation of the hypothesis: Antigenic shift of influenza occurs is a result of genetic reassortment between animal and human influenza A viruses. It is suggested the viruses spread from the migratory birds to other avian species such as chicken or ducks along their migratory pathways. Solar activity has an influence on terrestrial climate in terms of temperature, rainfall, storms and finally the biological systems. It was shown that the arrival dates of some migratory birds were delayed with increased sunspot numbers. This delay arrival may be associated with increased contacts with other susceptible birds in their migratory routes that facilitate genetic reassortment of the circulating influenza viruses. TEST THE HYPOTHESIS: Comprehensive reviews on both pandemics and possible pandemics of influenza were searched. International sunspot numbers were obtained from the World Data Center for Sunspot Index, Belgium and used to detect pandemics by binomial test. Five comprehensive reviews were found and the agreements on pandemics were good to excellent. Sensitivity of using Sunspot Number more than 50 (SSN>50) to detect pandemics increased as the levels of agreements increased. In stringent criteria, two pandemics might have occurred in the 18th century (1729-1733 and 1781-1782), two in the 19th century (1830-1833 and 1889-1892) and three in the 20th century (1918-1920, 1957-1958 and 1968-1969). The sensitivity of using SSN>50 to detect influenza pandemics was 85.7% (95%CI=59.8-100%, p=0.019). The specificity was 51.2% (95%CI=35.9-66.5%).
Implications of the hypothesis: On top of virological and epidemiological surveillance, sunspot cycles may be an inexpensive and easy method to detect influenza pandemics. The next high risk period will be around 2008-2013 and it may suggest us to be more alert and be prepared in order to minimize unnecessary deaths as a result of influenza.