Spatial Spread Of Measles In China

Measles is a highly infectious acute infectious disease,a serious threat to human health.In recent years,the immunization coverage of measles in China has exceeded95%,but measles is still prevalent repeatedly in China.At present,the research on the prevalence of measles in China focuses on the epidemiology,serology and other fields,but the research on the transmission mechanism of measles is still limited.Our previous study found that the prevalence of measles in different regions in China is strongly correlated,so it is necessary for us to start from the spatial transmission power,analyze the characteristics and dynamic mechanism of the spatial transmission of measles in China,and find the cause of the delay in the elimination of measles in China under the condition of high immunization coverage.This paper first analyzes the characteristics of the geographical space spread of measles in China.In this study,we decomposed the reported measles cases in 31provincial administrative regions from 2004 to 2016 using wavelet analysis tools,analyzed the measles epidemic periodicity in each region,and established the correlation function between measles epidemic correlation and geographical distance based on the phase coherence of wavelet analysis.At the same time,the beginning time of measles epidemic in each region was calculated by wavelet decomposition method,and the spatial-temporal traveling waves of measles before and after mass immunization in 2010 were constructed.We also studied the correlation between precipitation,temperature,relative humidity and the prevalence of measles by cross wavelet analysis.Secondly,taking Shandong Province as an example,a mathematical model of measles aggregated population including infective infection was constructed,and the least square method was used to estimate the seasonal transmission rate of measles in Shandong Province.According to the parameter estimation results,the seasonal variation of basic regeneration number（R₀）and effective regeneration number（R_e）of measles were calculated.Finally,we made several hypotheses based on imported infected persons and seasonal transmission rate,and constructed different aggregate population models to analyze the impact of imported infected persons and seasonal transmission rate on measles prevalence in Shandong Province.The results showed that:1)the prevalence of measles in the whole country showed a strong annual cycle,and only Shandong Province showed a double periodicity of annual cycle and three-year epidemic cycle;2)the prevalence of measles in 31 provinces had a high correlation within 1000 km,and decreased with distance.At the same time,before the implementation of intensive immunization in2010,there were two spatial-temporal travelling waves,of which the North China travelling wave was the main travelling wave.Implement strengthened after immunization,spatial-temporal travelling wave number increased to four;3)climate factors of precipitation temperature and relative humidity factors associated with measles epidemic periodic present strong,but there is no causal relationship;4)infection and the infection rate seasonal flooding in floating population（of infection rate increased 190%during Spring Festival）is the important factors that affect the measles epidemic in Shandong Province.At the same time,we found that the effect of measles immunization in Shandong province in 2010 was not significant;5)the average values of measles R₀and R_ein Shandong Province were 9.13 and 0.82respectively.R₀and R_eincreased sharply during the Spring Festival travel rush,in which R_ewas higher than 1 during the Spring Festival travel rush and rapidly decreased to less than 1 after the Spring Festival travel rush.The high infection rate during the Spring Festival travel rush inter plays with the inflow of infected persons,which is the key reason why measles cannot be eliminated in Shandong Province,and may also be the reason for the persistent measles epidemic in other areas with large migration of people with high immunization coverage.