POPULATION IMMUNITY TO INFLUENZA VIRUS A(H1N1)pdm09, A(H3N2) AND B IN THE ADULT POPULATION OF THE RUSSIAN FEDERATION LONG-TERM RESEARCH RESULTS

Abstract

Analysis of changes in the population immunity level in adults for more than 20 Russian cities, collaborating with the Federal Center for Influenza, to circulating influenza viruses A(H1N1)pdm09, A(H3N2) and B in the period from 2009 to 2015 performed. By the beginning of the pandemic (October 2009) the population of Russia was almost seronegative to influenza A(H1N1)pdm09 virus. After the pandemia first wave mean geometric titers (GMT)s of antibodies to the pandemic virus increased by 2.6 times, after the second one by 4.9 times in comparison with initial GMT (1:5.5). A consistent increase in GMTs antibody after each of the subsequent seasons of active circulation of pandemic virus was observed reaching the maximum (1:41) by April 2013, after the next epidemic caused by this virus. The proportion of people with protective antibody titers in October 2009 to already started circulating influenza A(H1N1)pdm09 virus was 8.2%, to influenza A(H3N2) virus — 58.3%, and influenza B virus — 59.7%. Level of population immunity in adults to seasonal influenza A(H3N2) and B viruses throughout the observed period was significantly higher than to influenza virus A(H1N1)pdm09. The percentage of persons with protective antibody titers during the observed period varied for virus A(H3N2) in the range from 58.3 to 75.5%, for influenza B virus — from 59.7 to 82.3%. Accordingly, incidence rate for ILI and ARI in adult groups the population during influenza epidemic caused by these pathogens was lower than in the epidemics, associated with active circulation of influenza A(H1N1)pdm09 virus. The data obtained can be used in influenza forecasting for the upcoming season regarding the etiology and the expected epidemic intensity need for the relevant preventing measures development to decrease the burden from influenza.