Study On The Trend Of Morbidity And Mortality Of Targeted Communicable Diseases At Different Stages Of National Immunization Program

ObjectAnalyze the change of the main targeted communicable diseases of National Immunization Program (NIP), to evaluate the effect on controlling diseases by implementing NIP.MethodAccording to the time when the vaccine come out and the history of NIP, we devided the period of year 1950 to 2014 into 4 stages, that are, pre-vaccine stage, pre-planned immunization stage, plan immunization stage and expanded programing on immunization stage (EPI). Choosing measles, polio, pertussis, diphtheria, meningitis and Japanese encephalitis (six disease) as representatives, we conducted the analysis by using the methods as follows:1. Discriptive epidemiology method was used to demonstrate the epidemic characteristics on temporal and spatial distribution of six diseases, and analyze the seasonal feature by concentration degree analysis.2. Conduct the spatial auto-correlation analysis, both global and local, to detect the characteristic of spatial distribution of six diseases.3. Analyze the time series data by using the interrupted time series (ITS) analysis to find the influential point and trend change.4. Conduct dynamic infectious mathematic modelling method, taking the population heterogeneity and cyclical transmission rate into consideration, to estimate the real situation of measeles occurrence.Results1. All the six diseases revealed a dramatic decline both in morbidity and mortality after vaccine became available. Polio exhibited the biggest decrease in the pre-planned immunization stage (40.6%). In the planned immunization period, measles showed the largest decline (94.73%), and Japanese encephalitis got the smallest decrease(44.8%), the other 4 disease fluctuated between 87.5% and 96.9%. compared with the pre-vaccine period. When compareed the EPI period with the pre-vaccine period, the decline of all the 6 diseases were more than 98%, expecially, diphtheritis and poliolytis was eradicated.2. The ITS analysis found that, in the pre-planed immunization period, polio (p<0.01), meningitis (p<0.01), Japanese encephalitis (p<0.01) and measles (p=0.02) showed a significant change in the incidence trend against time, compared the pre-vaccine period. Compared with the pre-plan immunization stage, pertussis (p<0.01) and diphtheritis (p<0.01) showed a significant trend change in planed immunization period, which indicated the rate of decline in incidence has been speeded up after the impletment of planed immunization. While polio (p=0.27) and measles (p=0.41) showed no significant difference.3. All 6 diseases displayed different type of spatial clustering, mainly in High-High cluster, in pre-vaccine period, pre-planed immunization period and planed immunization period. The number of provinces covered by high-clusters were 21,18, 13.and 6, in each one of the 4 stages, and it showed a dramatic decrease in the EPI stage.4. The SIR modelling was used to estimate the situation of measles from year 1950 to 2014, the estimated parameters in the mathematic modelling were a1=1.74, b1=3.28, c1=-1.12 for the of<5 year group, and a2=1.67, b2=5-64,c2=-1.01 for the≥5 years group. The difference between the reported cases and the estimated cases of measles are 81.3%,68.0%,66.4% and 56.2% in the 4 stages. Compared with pre-vaccine stage, the incidence of measles showed a 34.9% decline in the pre-planned immunization stage,94.7 in the planned immunization stage and 99.4% in the EPI stage.ConclusionThe vaccines decreased the morbidity and mortality of the 6 targeted diseases in the study, vaccination is the most important way to control diseases. The implementation the planned immunization acceletated the decrease of morbidity and mortality. Improving vaccination coverage is the key point to control diseases. The planned immunization policy is very effective in decreasing the morbidity. The EPI stage keeps the morbidity in a very low level, weakens the periodicity of epidemics, prevent the large scale outbreak.