High Titers of Hemagglutination Inhibition Antibodies against 2009 H1N1 Influenza Virus in Southern Iran

Abstract

<b>Background</b>: Pandemic flu had at least two waves in Iran. Knowing how many of the general population were already exposed to this infection has a major impact on na-tional preventive measures. As of December 30, 2009, a total of 3672 confirmed cases of human infection with a novel Influenza A (2009 H1N1) virus had been reported in Iran with 140 deaths. <br/><b>Objective</b>: In this study we aim to measure, as a pilot study, the seroprevalence of positive antibody titer (humoral immunity) against 2009 H1N1 virus in Iranian population in Shiraz, Southern Iran. <br/><b>Methods</b>: Through cluster random sam-pling of families residing in Shiraz, 2553 subjects were selected and after a medical in-terview blood samples were taken and checked for polyclonal antibody against 2009 H1N1 antigen using hemagglutination inhibition assay. An antibody titer of more than 1:40 dilution was considered positive. Data were analyzed considering the demographic characteristics of the population and were compared among different age groups. <br/><b>Results</b>: 1504 (58.91%) samples were tested positive for the presence of polyclonal an-tibody against 2009 H1N1 virus. The prevalence of positive titers were significantly higher in 60 to 64 years old group and significantly lower in 20 to 24 years old group (p<0.05). Data did not differ based on other demographic characteristics or the history of flu like illnesses in the past 6 months. <br/><b>Conclusion</b>: High seroprevalence of antibody against 2009 H1N1 in the sera of our subjects describes either a high level of pre-existing immunity against H1N1 in Iranian population or a high rate of asymptomatic infection in our area compared to other countries.