Regional characteristics of influenza seasonality patterns in mainland China, 2005-2017: a statistical modeling study

Objectives: To quantify the seasonal and antigenic characteristics of influenza to help understand in-fluenza activity and inform vaccine recommendations.Methods: We employed a generalized linear model with harmonic terms to quantify the seasonal pattern of influenza in China from 2005-2017, including amplitude (circulatory intensity), semiannual periodicity (given two peaks a year), annual peak time, and epidemic duration. The antigenic differences were dis-tinguished as antigenic similarity between 2009 and 2020. We categorized regions above 33 degrees N, between 27 degrees N and 33 degrees N, and below 27 degrees N as the north, central, and south regions, respectively.Results: We estimated that the amplitude in the north region (median: 0.019, 95% CI: 0.018-0.021) was significantly higher than that in the central region (median: 0.011, 95% CI: 0.01-0.012, P < 0.001) and south region (median: 0.008, 95% CI: 0.007-0.008, P < 0.001) for influenza A virus subtype H3N2 (A/H3N2). The A/H3N2 in the central region had a semiannual periodicity (median: 0.548, 95% CI: 0.517-0.577), while no semiannual pattern was found in other regions or subtypes/lineages. The antigenic similarity was low (below 50% in the 2009-2010, 2014-2015, 2016-2018, and 2019-2020 seasons) for A/H3N2.Conclusion: Our study depicted the seasonal pattern differences and antigenic differences of influenza in China, which provides information for vaccination strategies.(c) 2022 The Author(s). Published by Elsevier Ltd on behalf of International Society for Infectious Diseases. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )