Study On Molecular Characteristics, Excess Mortality And Immunization Strategies For Influenza A (H1N1) Pdm09

Background&ObjectiveAfter the first description of a novel Influenza A (H1N1) pdm09(pH1N1) in Mexico and the United States in April2009, the virus rapidly spread worldwide, resulting in considerable human suffering and economic burden.Then the spread of pH1N1had been moderate since the virus did not undergo critical antigenic change and the host acquired immunity to pH1N1with the mass vaccination. However, in2013, the number of positive isolations of pH1N1began to rise again in Guangzhou, which caused concerns for possible epidemic. With the aim of providing the reference for the prevention and control of pH1N1, we need to carry incessancy surveillance about the pH1N1molecular epidemiological and the studies of pH1N1antigenic variation.Seasonal epidemic and pandemic influenza can caused substantial morbidity and mortality worldwide. The accurate evaluation of this mortality burden is important for the prevention of pH1N1. Because of that the flu diagnosis is usually based on clinical symptoms rather than the laboratory tests and cause death not only due to "flu and pneumonia" but also others serious complications. The death burden of the flu will be greatly underestimated only through analyzing the death of "flu and pneumonia". Foreign research commonly used mathematical models to estimate the influenza-associated excess mortality to accurately evaluate the mortality death. However, relative data were scarce in tropical regions. We aimed to estimate pH1N1-associated excess mortality in Guangzhou, China and assess the different excess mortality due to other subtypes of viruses.The World Health Organization (WHO) contends that annual vaccination prior to the influenza epidemic peak is currently the principal strategy for preventing influenza. Since2010-2011, the pH1N1strain have added in the seasonal trivalent inactivated influenza vaccine(TIV) to protect against pH1N1. The protective role of TIV is also closely related to the population vaccine coverage. Regular surveys of flu vaccine coverage can make a better understanding of the situation about the population’s level of vaccination and immunity population. Most of the current domestic coverage investigation mainly adopts questionnaire survey, which is difficult to avoid selection bias and information bias. Children are susceptible to be infected by influenza, about40%preschool children and30%school child infected by influenza each year in China. Serious outcomes of influenza infection can result in serious influenza complications or even death, especially those with certain health conditions. Therefore, it is necessary to assess the level of TIV coverage in this population.Vaccine effectiveness can be assessed by immunogenicity, efficacy and effectiveness. Postmarketing vaccines have been assessed the safety and validity by preclinical study and phase Ⅰ, Ⅱ, Ⅲ clinical trials. However, these studies are not possible to assess epidemiological effect, immune persistence and the aspect of health economics. Because of that the factors that affect the protection of the actual effect after vaccination is numerous such as the matching degree between influenza virus vaccine strains and popular plant, the time interval of vaccination and epidemic period and the inoculation rate of population, it is necessary to conduct a evaluation of the post-marketing epidemiologic effectiveness based on the endpoint of disease. At present serological study are overwhelming and the observation time too short to be able to make a exact evaluation for the epidemiological effect of vaccine, the immune persistence and benefit and risk of health economics. In conclusion, the influenza vaccine effectiveness is not completely assessed, and further postmarketing studies among children are needed.Guangzhou is located in south China with a subtropical monsoon climate, viral influenza strains that persist in this region could potentially serve as year-round reservoirs of global genetic diversity. On account of the present situation and the problems listed above, study on Excess Mortality of Influenza, relationship between the epidemiological feature of pH1N1and HA genetic variation characteristics, vaccine effectiveness against pH1N1and inoculation rate investigation of children based on Vaccine registration information have been conducted. The concrete results are as following:Chapter1Study on molecular characteristics for influenza A (H1N1) pdm09and genetic characteristics of hemagglutinin.Through epidemiologic and molecular bioinformatics methods, we analyze the molecular epidemiological characteristic, the gene molecular evolution and the protein variation of pH1N1in Guangzhou to provide a stream of basis for influenza.MethodsInfluenza surveillance data were collected and analyzed to describe the epidemiologic feature of pH1N1in Guangzhou during2009-2013.The nucleotide sequences of HA gene of pH1N1viruses were obtained by using RT-PCR and gene sequencing techniques. The characteristics of HA sequences were analyzed with bioinformatics software.Results1. The pH1N1epidemiological characteristics of time showed that the number of pH1N1case increased month by month since May2009when the first imported case was reported, and reached the peak in November, since then the number of case decreased with most of them to be sporadic cases, and there was no case reported after2011May. However pH1N1became predominant strain again since January2013. The regional distribution showed that the infection Component ratio of urban was higher than that of urban-rural fringe and suburb region. The population distribution showed that the infection Component ratio of male was higher than that of female while that of children and adolescents higher than that of elderly group.2. In the respect of subtypes monitoring, H3N2and pH1N1were mainly pandemic strains and in Guangzhou during2009-2010the latter remained a potential pandemic threat, while H3N2and B (H1N1) during2010-2011. And during2011-2012, pH1N1took hold in the first quarter of a year and then pH1N1afterwards. H3N2and B (H1N1) were predominant and pH1N1Had not been detected during2012-2013. pH1N1became a predominant train during2013for a whole year. The five influenza epidemic monitoring season were respectively April-December, January-May, January-June, February-August and February-June and more than2peaks of the pandemic had been detected in most of the monitoring seasons.3. The HA of pH1N1during2009-2013of Guangzhou had multiple branches on the gene evolutionary process and shared the same branch with the other strains all over the world at the same time. The strains of2009and2010shared the same branch and had the high homo logy with A/California/07/2009. The strains of2011was a nearly ones after2013while one of those preserved. Amino acid sequence variation analysis showed15sites of the amino acid residues were not completely consistent from2009-2013which were respectively site4,5,6,7,8,9,10,11,12,65,103,145,421,499and526.ConclusionThe pH1N1virus strains of2009-2013were so closely related with A/California/07/2009in2009and2010worldwide. pH1N1virus was highly homologous but some amino acids sites of that mutated. H3N2, pH1N1, B (H1N1) were alternating with each other in Guangzhou during2009-2013. pH1N1had a higher morbidity in urban region and children and adolescents population. Chapter2Study on influenza A (H1N1) pdm09-associated excess mortality in GuangzhouWe aimed to estimate the influenza-associated excess mortality due to pHlNl and other subtypes of viruses across Guangzhou, which contribute to make a better understanding of the influenza and mortality burden of that.MethodsWe estimated influenza-associated excess mortality due to5-outcome including pneumonia and influenza (P&I), circulatory and respiratory disease (CRD), all cause deaths (AC), ischemic heart disease (IHD) and chronic obstructive pulmonary disease (COPD) according to weekly numbers of deaths and influenza surveillance data through negative binomial regression model during2010-2012.Results1.The annual excess mortalities of5-outcomes (AC, CRD, P&I, COPD and IHD) during3influenza seasons are retrospectively14.72(95%CI,12.12-17.31) per100,000,11.40(95%CI,9.38-13.42) per100,000,2.26(95%CI,1.86-2.67) per100,000,2.81(95%CI,2.31-3.32) per100,000and2.21(95%CI,1.78-2.64) per100,000. Annual excess mortality of5-outcome in≥65group are12-15times higher than in total population, that of AC is the highest, and CRD secondly.2.During2010-2012, the excess mortality of total population for AC, CRD, IHD, COPD and P&I resulted from pH1N1is3.99per100,000,3.06per100,000,0.72per100,000,0.50per100,000and0.40per100,000. People aged>65years made a major contribute to the excess mortality of5-outcome caused by pH1N1. Except IHD(12.01,95%CI,6.98-17.04per100,000), the excess mortality for AC, CRD, P&I and COPD caused by pH1N1is the lower than other two subtypes.Conclusion Influenza pH1N1led to marked excess mortality in every season during2010-2012, which posted the greatest threat to≥65group. Influenza virus Type B accounted for the highest excess mortality than pH1N1. The study indicates that it attachs importance to vaccinating in subtropical regions during influenza season, especial for≥65group in order to reduce the excess mortality. Chapter3Trivalent inactivated influenza vaccination coverage among children aged6-107months in Guangzhou, China.We aim to estimate the influenza vaccine (TIV) coverage rate and factors of children aged6-107months selected from the Children’s Expanded Programmed Immunization (EPI) Administrative Computerized System.MethodsInfluenza vaccine information and basic information of children aged6-107months up to investigation date were collected from the EPI by stratified random sampling.Results1. The TIV vaccination rate of13399children aged6-107months was37.7%, and the fully vaccination rate was was2.3%only.2. Age, gender, region and household factors affected the TIV vaccination rate. Those who are≥60months, female, downtown or local performed higher rate of one or two dose vaccination.3. The median month of first-dose vaccination was14months. The ratio of the incorrect time-lag between two dose of TIV ranged from1.2%to14.3.ConclusionThe coverage rate of TIV in Guangzhou was not enough to emerge herd immunity effects, especially the fully vaccination rate is extremely low; There are lingering problems about the delayed first-dose time and incorrect time-lag between two dose. More action should be taken in order to improve the coverage rate of TIV especial for fully vaccination rate. It’s of importance to strengthen the immunization affairs aiming at low-rate population and standardize the vaccination program for the health of children in Guangzhou. Chapter4Effectiveness of trivalent inactivated influenza vaccine against influenza A (H1N1) pdm09in children during2013in Guangzhou, China, a case-control studyWe aimed to estimate the effectiveness of TIV for children aged6-107months during influenza epidemic period of2013seasons and to provide the scientific basis for control efforts of pH1N1.MethodsChildren aged6-107months diagnosed as pH1N1virus positive and confirmed by laboratory (Real-time PCR positive) during influenza season in2013across Guangzhou were collected and assigned to case group, and cases which are pH1N1negative were assigned to negative control group. Non-paired design was conducted between case group and negative control group. The healthy controls without influenza symptoms were confirmed by researchers, and cases and health control groups were1:1matched by birth date, gender, and outpatient services of vaccination. The pH1N1epidemic periods were defined by the surveillance of circulating viral strains. The pH1N1cases were obtained from the surveillance system. Negative controls were randomly collected from pH1N1-negative patients confirmed by Guangzhou CDC laboratory. Health controls were randomly sampled from the Children’s Expanded Programmed Immunization (EPI) Administrative Computerized System. Non-conditional logistic regression was conducted for case-negative design, and conditional logistic regression was applied for1:1paired case-health design. Confounding factor (age, gender, region, census register and vaccination age) were adjusted for VEs and95%confidence interval.Results1. We analyzed the vaccination information for2126sets of subjects, whose average age of onset was38.7±25.3months and average age47.0±24.9months. Cases mainly were local children and male and Baiyun district own the most cases. Health control followed the same pattern.200children of negative group were analyzed and there was no difference between case and health groups on gender, region and census register except average age (42.2±20.6months). The coverage rate of pH1N1influenza vaccine was8.5%, which lower than health control (17.2%) and negative control (19.5%).2. The VE for pH1N1of health control during2013was58.3%(95%CI,47.9-66.6) and familiar with that of negative control (53.7%95%CI,30.5-69.2).3. Vaccine for36-39months group had a higher VE than6-35months group and60-107months group (78.7%95%CI,51.8-90.6VS65.0%95%C,52.1-74.3and53.4%95%CI,22.8-71.8). Full vaccination provided more protection than partial vaccination among children aged6-35months (74.5%(95%CI,61.6-83.0)vs.49.9%95%CI,24.5-66.8). VE of male was lower than that of female (63.4%95%CI,50.6-72.9VS73.3%5%CI,50.7-85.6). Vaccine provided more protection in pre-epidemic period than in post-epidemic period (56.6%95%CI,31.9-72.3VS45.3%95%CI,15.7-64.5).4. The effect of current vaccine might be influenced by the previous vaccine, and the combined immunization of2013and2012-2013,2013and2011-2012increased most obviously (75.5%95%CI,57.8,85.8AND84.9%95%CI,53.8-95.1). However, VE of2012-2013(46.3%95%CI,26.6-60.8)) was lower than that of2013.5. The VE decreased gradually from76.8%(95%CI,66.0-84.1) in1-2months after vaccination to50.3%(95%CI,31.0-64.2) in3-4months after vaccination.ConclusionIt is feasible to adopt healthy children as a control to assess the VE of TIV. The TIV had moderate protection against pH1N1for children aged6to107months. Annual,full and timely vaccination prior to the influenza epidemic peak should be encouraged for children aged6to107months.