Geographic and intra-year seasonal variations in influenza-related health outcomes across mainland China: a systematic review and spatio-temporal analysis

Authors: Charlie Diamond, Hui Gong, Fiona Yueqian Sun, Yang Liu, Billy J. Quilty, Mark Jit, Juan Yang, Hongjie Yu, W. John Edmunds^†, Marc Baguelin^†

Correspondence to: charlie.diamond@lshtm.ac.uk

^† authors contributed equally

Abstract

Background

China experiences large variations in influenza seasonal activity. We aim to update and improve the current understanding of the geographic and within-year variations of influenza to provide evidence for the planning and optimisation of healthcare strategies.

Methods

We conducted a systematic review and spatio-temporal meta-analysis to assess the geographic and seasonal variations of four influenza-related health outcomes. We searched English and Chinese databases for articles reporting time-series data on the four influenza-related outcomes at the sub-national and sub-annual level. After synthesizing the data, we reported on the mean monthly rate, epidemic onset, duration, peak and intensity.

Results

We included 247 (7.7%) eligible studies in the analysis. We found intra-year influenza patterns to vary across mainland China in relation to latitude and geographic location. High-latitude provinces were characterised by having short and intense annual winter epidemics, whilst most mid-latitude and low-latitude provinces experience semi-annual epidemics or year-round activity. Subtype activity varied across the country, with A/H1N1pdm09 and influenza B occurring predominantly in the winter, whereas A/H3N2 activity exhibited a latitudinal divide with high-latitude regions experiencing a winter peak, whilst mid and low-latitude regions experienced a summer epidemic. Epidemic onsets and peaks also varied, occurring first in the north and later in the southeast. We found positive associations between all influenza health outcomes. In addition, seasonal patterns at prefecture and county-level broadly resembled their wider province.

Conclusions

This is the first systematic review to simultaneously examine the seasonal variation of multiple influenza-related health outcomes at multiple spatial scales across mainland China. The seasonality information provided here has important implications for the planning and optimisation of immunisation programmes and healthcare provision, supporting the need for regional based approaches to address variations in local epidemiology.

Data avaiablity

All data extracted is catalogued in DES/Data_look_up.xlsx and available in the cleandata/ folder with the corresponding csv code.