Seroepidemiological analysis of influenza pandemics in Shizuoka Prefecture and all Japan

(1) Seroepidemiological analysis of influenza pandemics (1986-2003) in Shizuoka Prefecture and all Japan revealed differences in geographical, annual, seasonal, and age distributions. (2) For 17 years, the pandemics generally began at the 50th week every year showing over 1.0 patient/clinic, reached the peak at 5th week the following year, and ended over 10-15th week. Two big A/H3N2 pandemics were seen in 1989/1990 and 1997/1998 seasons, claiming over I million patients in Japan. (3) As herald strains, AM3N2 strains (A/Sydney-like) were found in October 1999, and B strains (B/Victoria- and B/Yamagata-like) were detected in July and November 1998 and, in August and December 2000 in Shizuoka. B/Shizuoka/1/98 strain was registered internationally as a vaccine-recommended strain. (4) A/H3N2 and B viruses were detected in 55-78% of flu patients (almost under 10 years) with encephalopathy in 1999/2000 and 78-91% in 2000/2001 by MDCK and reverse transcription polymerase chain reaction (RT-PCR) methods. (5) High hemagglutination inhibition (HI) titers over 40 in 250 persons were shown against A/Sydney/5/97 (H3N2), A/Yokohama/8/98 (H3N2), A/Panama/2007/99 (H3N2) and A/Moscow/10/99 (H1N1) strains, while low titers showed against A/Beijing/262/95 (H1N1) and A/New Caledonia/20/99 (H1N1), and B/Beijing/243/97, B/Shangdong/7/97 and B/Yamanashi/106/98 strains in 1998-2000. (6) In anti-HA titers against A/H3N2, A/H1N1 and B subtypes, clear generation gaps were observed between children (0-19 years), adults (20-59 years) and old men (over 60 years). (7) The pandemics are dependent on host immunity (acquired and vaccinated) and climatic conditions (low temperature, low humidity and limited rainfall), considering highly pathogenic avian influenza (HPAI) viruses (A/H5N1, A/H7N7) like severe acute respiratory syndrome (SARS) corona virus in 2002-2003. (C) 2004 Published by Elsevier B.V.