Hepatitis B vaccine response in obesity: a meta-analysis (Protocol)

Transcription

1 Hepatitis B vaccine response in obesity: a meta-analysis (Protocol) Wei Fan a,, Xiao-fang Chen b,, Chao Shen a, Zhi-rong Guo a, *, Chen Dong a, * Contents HEADER... 1 ABSTRACT... 1 BACKGROUND... 1 Description of the condition... 1 How obesity might work on the condition... 2 Why it is important to do this meta-analysis... 2 OBJECTIVES... 2 METHODS... 2 Criteria for considering studies for this meta-analysis... 2 Types of participants... 3 Types of exposure and outcome measurement... 3 Search methods for identification of studies... 3 Selection of studies... 3 Data extraction and management... 4 Quality assessment of the selected studies... 4 Measures of effect estimates... 4 Dealing with zero cells (only when unadjusted estimates are used)... 4 Assessment of heterogeneity... 4 Data synthesis... 5 ACKNOWLEDGEMENTS... 5 CONTRIBUTIONS OF AUTHORS... 5 DECLARATIONS OF INTEREST... 5 SOURCES OF SUPPORT... 5 REFERENCES... 5 APPENDICES... 7

2 HEADER Hepatitis B vaccine response in obesity and overweight: a meta-analysis (Protocol) Wei Fan a,, Xiao-fang Chen b,, Chao Shen a, Zhi-rong Guo a, *, Chen Dong a, * a Department of epidemiology, School of Public Health, Soochow University, Suzhou, , China. b Suzhou Industrial Park Centers for Disease Control and Prevention, Suzhou, , China. Zhirong Guo. address: guozhirong28@163.com * Corresponding author. Chen Dong. address: cdong@suda.edu.cn; These authors contributed equally to this work. Contact address: Zhi-Rong Guo Department of epidemiology School of Public Health Medical College of Soochow University 199 Ren ai road Industrial Park District Suzhou Jiangsu China fax: guozhirong28@163.com Chen Dong, Department of epidemiology School of Public Health Medical College of Soochow University 199 Ren ai road Industrial Park District Suzhou Jiangsu China fax: cdong@suda.edu.cn ABSTRACT Abstract is not available in this paper. The objectives as follows: The aim of the present study is to assess the impacts of obesity and overweight on the responses of hepatitis B vaccine. BACKGROUND Description of the condition Hepatitis B is a contagious liver disease caused by hepatitis B virus (HBV). Globally, more than 240 million people have chronic liver infections and more than 780 thousand people died of acute or chronic HBV infection every year [1]. Hepatitis B immunization is the most effective and economical way to prevent the virus infection. A great deal of evidence has proved that more than 90% of populations, especially children and infants, can be protected from the virus infection by hepatitis B vaccination. However, some vaccinees cannot get protective antibodies to hepatitis B surface antigen (anti-hbs) (higher than 10 IU/L) because of many risk factors such as older age, renal diseases and inappropriate administration of the vaccination [2-5]. Previously, obesity has been reported as a risk factor for the poor vaccine efficacy [6]. The first study on the relationship between obesity and hepatitis B vaccination response was conducted by Weber et al. in The authors reported that a higher body mass index (BMI) would develop a poor antibody response in health care workers [7]. In 2008, Dinelli et al. reported that a case could get seroprotection of hepatitis B vaccine after a dropped BMI [8]. Considering both obesity/overweight and chronic HBV infection are serious public health issues worldwide, more studies should be performed to investigated the effects of obesity/overweight on the hepatitis B vaccines responses. 1

3 How obesity might work on the condition The impacts of obesity on immunologic response to hepatitis B vaccine might be involved with a series of complex mechanisms. First, impaired immune system has been found in both obese animals and humans [9]. Young et al. reported that obesity was significantly associated with the decreased naïve T-cells from thymus [10]. Compared to the lean controls, diminished numbers and decreased activities of CD8 + T-cells and NK cells were observed in obesity subjects [11-14]. In addition, Nieman et al. reported that the proliferations of T- and B-cell decreased in the obesity humans with mitogen stimulation [15]. Second, since the skin thickness of the obese subjects were thicker than those in non-obesities, needle length used for vaccination might be as a potential risk attributed to the poor response in obese individuals. [16]. Last, it is well known that obese individuals usually suffer from a chronic low-grade chronic inflammatory state, which might be also involved in the lower responses to HBV vaccines [17, 18]. Although several potential mechanisms behind the lower hepatitis B vaccine responses in obesity have been described before, the arguments have not been well cleared and more studies are stilled needed to test these results. Why it is important to do this meta-analysis Meta-analysis is a technique to combine the results from independent studies, which gives enhanced power to interpret the conclusion. Moreover, it has been deemed that the conclusion made by meta-analysis is statistically stronger than any single included study did, due to increased numbers of subjects, greater diversity among subjects, and accumulated effects and results. Thus, Meta-analysis is widely used to establish statistical significances in the studies with controversial results. In spite of the significant associations were observed between the obesity and the poor response to hepatitis B vaccines previously [7, 16], there were still other investigators failed to replicate these results [19, 20]. Moreover, although some studies suggested that there was a decreased immune response to hepatitis B vaccines in obesity, the results should be further analyzed because of very small sample size [16, 21], specific populations (such as healthcare workers and women) [16, 22-24], different vaccination schedules [20, 25, 26] and different methods used for non-responsiveness analysis in the previous studies. Since the conclusions drawn from the given studies might be limited, we performed the present meta-analysis study to further clarify the impact of obesity/overweight on the immunologic response to hepatitis B vaccines and to enhance the statistical power for the previously reported estimates. OBJECTIVES The aim of the present meta-analysis is to assess the association between obesity/overweight and hepatitis B vaccination with reliable data, and to provide the theoretical evidences for the administration of vaccination improvement. METHODS Criteria for considering studies for the meta-analysis All types of the studies meet the following criteria were included in the present meta-analysis: (1) Studies on 2

4 the relevant topics published on peer-reviewed journals with full-text available. (2) Studies on the response to recombinant hepatitis B vaccines in vaccinees with and without obesity. Subjects with anti-hbs lower than 10 IU/L after vaccination were defined as non-seroprotected cases. (3) The present analysis only included the subjects vaccinated with recombinant hepatitis B vaccines, because the safety of other vaccines, such as plasma derived vaccines (PDV), did not gain enough acceptances from the general public [27]. (4) The vaccination program was a schedule of no less than 2-dose. Types of participants Individuals with apparent health status will be included in the present meta-analysis. However, participants will be excluded for the following reasons: (1) women in pregnancy. (2) HBsAg positive or anti-hbc positive. (3) Received hepatitis B vaccination in any schedule before or no clear vaccination history. (4) With other diseases might affect the immune response to HBV infection, such as immunodeficiency (HIV-infection) and hemodialysis, etc. Types of exposure and outcome measurement Obesity in this meta-analysis will be determined by body mass index (BMI). We defined the individuals with obesity if they met the definition used in the study in which they participated. When multiple BMI strata were available, BMI 30 kg/m 2 was used as a default definition of obesity for study participants [28], and if possible, BMI<25 kg/m 2 was used as the reference. Because the definition of obesity might be different among included studies, subgroup analyses will be performed to evaluate the estimations of the groups with different cut-off values of BMI. All subjects included in the present analysis should have completed vaccine schedules (2 or more doses). One month after the complete vaccination schedules, subjects with 10 IU/L of anti-hbs were classified as responders (seroprotected). In addition, in the present study, we will also keep a watchful eye on the adverse events induced by the vaccination in obese and non-obese population if certain information is available in the retrieved papers. Finally, the papers reported that (1) data can be listed as a form of 2-by-2 table, or (2) provided adjusted estimates and a measure of variance for immune response among obese subjects, compared with non-obese subjects, were considered qualified for the present analysis. Search methods for identification of studies Electronic search engines are preferred for convenience. We will search the papers on the topic interested in PubMed, EMBase, Web of Science and the Cochrane Library. The basic searching strategy will be a combination of several key words, such as obesity, Body mass index, BMI and hepatitis B vaccine and etc. Mesh terms will be also considered. Simultaneously, we will review the reference lists of the articles retrieved to gain more relevant data concerning the topic interested. Detailed searching strategies are displayed in Appendix 1 and Appendix 2. Of note, the hits will be updated when actually performing this work. Selection of studies Two authors will review each paper retrieved at the same time and make the decision on which study met the criteria (Appendix 3). Any disagreements will be resolved through discussion among the authors, or by adjudication with a third author. Excluded studies will be remarked with the reasons of exclusion. 3

5 Data extraction and management The extracted data of this meta-analysis will be entered in the electronic data sheet (Appendix 4). Quality assessment of the selected studies The quality of each study will be evaluated by several methods according to the type of the study it is: 1) The quality of cross-sectional studies will be assessed using the AHRQ (Agency for Healthcare Research and Quality) evaluation standard ( The AHRQ evaluation standard was a typical tool for the observational studies to assess the quality of prevalence studies in a meta-analysis. A total of 11 items are listed to assess the risk bias of these included studies, and detailed are shown in Appendix 5. 2) The quality of cohort studies will be evaluated by the Newcastle-Ottawa Scale (NOS) which is specially applied for assessing the quality of nonrandomized studies in systemic reviews and meta-analysis ( A 'star system' is developed in which a study is judged on three broad perspectives: the selection of the study groups, the comparability of the groups and the ascertainment of either the exposure or outcome of interest for case-control or cohort studies, respectively. The full mark is nine and each section will be scored with a maximum of one star except the section of comparability that can be scored two stars at most. Details have been listed in Appendix 6. 3) The risk of bias of randomized clinical trial (RCT) is evaluated by the Cochrane Collaboration's 'Risk of bias' tool which is supported in <Cochrane Handbook for systematic reviews> ( The tool is summarized in Appendix 7. We considered eligible studies to be of poor quality if they didn t get half of the total marks of the quality assessment tools (Cross-sectional: 6/11 Yes ; Cohort: 5/9 Stars; RCT: 3/6 Low risk ). Measures of effect estimates Pooled odds ratios and 95% confidence intervals will be calculated from the categorical data, and used to describe the risk of non-responsiveness of hepatitis B vaccines in obese population. Dealing with zero cells (only when unadjusted estimates are used) When unadjusted estimates are used, included data will be typed without zero cells. When an arm of a study contains no events (zero cell), we add a 0.5 value to each cell of the 2-by-2 table [29, 30]. However, the study will be discarded from this meta-analysis if there are no events in either exposure or control group of the study. These computations will be automatically done by statistical software, such as Stata. Assessment of heterogeneity We use both Q and I 2 statistics to assess the heterogeneity among the studies. An acceptable low degree of heterogeneity was considered if P>0.10 or I 2 <50%. When statistically significant heterogeneity are observed (P<0.10 and 50 I 2 75%), a random-effects model will be performed by using the DerSimonian-Laird (DL) approach [31]. In addition, a fixed-effects model using Mantel Haenszel method will be performed if these is no significant evidence to indicate the heterogeneity among the included studies (P>0.10 or I 2 <50%) [32]. When adjusted OR were provided by a single study, we will use the the inverse variance (IV) method to generate the 4

6 summary estimate if a low degree of heterogeneity is observed. We also try to perform the subgroup analyses to explore the source of heterogeneity if there is. We plan to assess the association between obesity and hepatitis B vaccines responses for the following subgroups: Various regions: Americans vs the Europeans, Asians, Australians and Africans. Various participants: health-care workers vs apparently healthy participants. Various vaccination schedules of the primary vaccination: 3 or more-dose vs 2-dose. Various injection routes: intramuscular (IM) vs intradermal (ID). Various vaccine or booster types: Engerix vs Recombivax HB and so on. Various types of research design. Data synthesis Stata statistical program (version 13) (Stata 13) will be used for the data analysis. Microsoft Access and Excel 2010 will be used for database management. ACKNOWLEDGEMENTS This work was supported by the project-sponsored by SRF for ROCS, SEM (K ), the Soochow University high-level scientific research foundation for the introduction talent (Q ), Pre-research foundation for nature science of Soochow University (Q ), and Research foundation for the prevention medicine in Jiangsu province (Y ). CONTRIBUTIONS OF AUTHORS Z Guo and C Dong conceived and designed the study. W Fan and C Shen will perform data collection. W Fan and X Chen will take charge of the quality assessment of the papers and perform the subsequent analysis. C Dong performed the major modification and language editing. DECLARATIONS OF INTEREST We declare that we have no conflict of interest. SOURCES OF SUPPORT Department of Epidemiology and Biostatistics, School of Public Health, Soochow University Research foundation for the prevention medicine in Jiangsu province (Y ) The Soochow University high-level scientific research foundation for the introduction talent (Q ) The project-sponsored by SRF for ROCS, SEM (K ) REFERENCES 1. WHO, Hepatitis B. Fact sheet.204, Updated July Website WHO( Chow, K.M., et al., Antibody response to hepatitis B vaccine in end-stage renal disease patients. Nephron Clin 5

7 Pract, (3): p. c Fabrizi, F., et al., Meta-analysis: intradermal vs. intramuscular vaccination against hepatitis B virus in patients with chronic kidney disease. Aliment Pharmacol Ther, (3): p Fisman, D.N., D. Agrawal, and K. Leder, The effect of age on immunologic response to recombinant hepatitis B vaccine: a meta-analysis. Clin Infect Dis, (11): p Sangare, L., et al., Intradermal hepatitis B vaccination: a systematic review and meta-analysis. Vaccine, (12): p Karlsson, E.A. and M.A. Beck, The burden of obesity on infectious disease. Exp Biol Med (Maywood), (12): p Weber, D.J., et al., Obesity as a Predictor of Poor Antibody-Response to Hepatitis-B Plasma Vaccine. Jama-Journal of the American Medical Association, (22): p Dinelli, M.I. and M.I. Moraes-Pinto, Seroconvertion to hepatitis B vaccine after weight reduction in obese non-responder. Rev Inst Med Trop Sao Paulo, (2): p Lamas, O., A. Marti, and J.A. Martinez, Obesity and immunocompetence. Eur J Clin Nutr, Suppl 3: p. S Yang, H., et al., Obesity accelerates thymic aging. Blood, (18): p Lynch, L.A., et al., Are natural killer cells protecting the metabolically healthy obese patient? Obesity (Silver Spring), (3): p O'Rourke, R.W., et al., Alterations in T-cell subset frequency in peripheral blood in obesity. Obesity Surgery, (10): p O'Shea, D., et al., Natural killer cells in obesity: impaired function and increased susceptibility to the effects of cigarette smoke. PLoS One, (1): p. e Tanaka, S., et al., T lymphopaenia in relation to body mass index and TNF-alpha in human obesity: adequate weight reduction can be corrective. Clin Endocrinol (Oxf), (3): p Nieman, D.C., et al., Influence of obesity on immune function. J Am Diet Assoc, (3): p Young, K.M., C.M. Gray, and L.G. Bekker, Is Obesity a Risk Factor for Vaccine n-responsiveness? Plos One, (12). 17. Beasley, L.E., et al., Body Composition Measures from CT and Inflammation. Obesity (Silver Spring, Md.), (5): p Das, U., Is obesity an inflammatory condition? Nutrition, (11): p Hagedorn, H.J., et al., Antibody response to hepatitis B vaccine in substance use disorder patients. Drug and Alcohol Dependence, (1): p Kulkarni, P.S., et al., Immunogenicity of a new, low-cost recombinant hepatitis B vaccine derived from Hansenula polymorpha in adults. Vaccine, (17): p Goldwater, P.N., Randomized, comparative trial of 20 mu g vs 40 mu g Engerix B vaccine in hepatitis B vaccine non-responders. Vaccine, (4): p Averhoff, F., et al., Immunogenicity of hepatitis B vaccines - Implications for persons at occupational risk of hepatitis B virus infection. American Journal of Preventive Medicine, (1): p Tolosa Martínez, N., et al., Factores asociados a una respuesta inadecuada a la vacunación contra la hepatitis B en personal sanitario. Revista Española de Salud Pública, : p Playford, E.G., et al., Intradermal recombinant hepatitis B vaccine for healthcare workers who fail to respond to intramuscular vaccine. Infection Control and Hospital Epidemiology, (2): p ul-haq, N., et al., Immunogenicity of 10 and 20 microgram hepatitis B vaccine in a two-dose schedule. Vaccine, (23): p Estevez, Z.C., et al., Immunogenicity and safety assessment of the Cuban recombinant hepatitis B vaccine in healthy adults. Biologicals, (2): p

8 27. WHO, More About Hepatitis B Vaccines. Vaccine Safety Basics-E-learning Course ( 28. WHO, Obesity and overweight. Fact sheet.311, Updated January Website WHO( Cox, D., The continuity correction. Biometrika, 1970: p Friedrich, J.O., N.K.J. Adhikari, and J. Beyene, Inclusion of zero total event trials in meta-analyses maintains analytic consistency and incorporates all available data. Bmc Medical Research Methodology, DerSimonian, R. and N. Laird, Meta-analysis in clinical trials. Control Clin Trials, (3): p Mantel, N. and W. Haenszel, Statistical aspects of the analysis of data from retrospective studies of disease. J Natl Cancer Inst, (4): p APPENDICES Appendix 1 Basic searching strategies for this topic #1 obesity OR overweight #2 BMI OR (body mass index) OR (quetelet index) #3 hepatitis B NOT (mice OR rats) #4 vaccine OR vaccination OR immunization OR (immune response) OR antibodies #5 #1 OR #2 #6 #3 AND #4 #7 #5 AND #6 #8 obesity [Mesh] OR overweight [Mesh] #9 body mass index [Mesh] #10 hepatitis B vaccine [Mesh] #11 #8 OR #9 #12 #11 AND #10 #13 #7 OR #12 Appendix 2 Detailed searching strategies performed in each searching engine. (update on v 16 th in 2015) Search Query Results Web of science # 7 #6 AND #5 310 actually Timespan=All years (Approximately Search language=auto 459) # 6 #4 AND #3 Approximately Timespan=All years Search language=auto # 5 #2 OR #1 Approximately Timespan=All years Search language=auto # 4 TOPIC: (vaccine) OR TOPIC: (vaccination) OR TOPIC: (immunization) OR TOPIC: (immune response) OR TOPIC: (antibodies) Approximately 7

9 Timespan=All years Search language=auto # 3 TOPIC: (hepatitis B) NOT TOPIC: (mice) NOT TOPIC: (rats) Approximately Timespan=All years Search language=auto # 2 TOPIC: (BMI) OR TOPIC: (body mass index) OR TOPIC: (quetelet index) Approximately Timespan=All years Search language=auto # 1 TOPIC: (obesity) OR TOPIC: (overweight) Approximately Timespan=All years Search language=auto Embase #7 #5 AND #6 453 #6 #3 AND #4 36,839 #5 #1 OR #2 569,429 #4 vaccine OR vaccination OR immunization OR 'immune response' OR antibodies 1,134,338 #3 'hepatitis b' NOT (mice OR rats) 122,162 #2 bmi OR 'body mass index' OR 'quetelet index' 267,616 #1 'obesity'/exp OR obesity OR 'overweight'/exp OR overweight 411,917 Pubmed #11 Search (((hepatitis B vaccines[mesh Terms]) AND (((obesity[mesh Terms]) OR overweight[mesh Terms]) OR body 192 mass index[mesh Terms]))) OR (((((((hepatitis B) NOT mice) NOT rats)) AND (((((vaccine) OR vaccination) OR immunization) OR immune response) OR antibodies))) AND (((((BMI) OR body mass index) OR quetelet index)) OR ((obesity) OR overweight))) #10 Search (hepatitis B vaccines[mesh Terms]) AND (((obesity[mesh Terms]) OR overweight[mesh Terms]) OR body 27 mass index[mesh Terms]) #9 Search hepatitis B vaccines[mesh Terms] 7861 #8 Search ((obesity[mesh Terms]) OR overweight[mesh Terms]) OR body mass index[mesh Terms] #7 Search ((((((hepatitis B) NOT mice) NOT rats)) AND (((((vaccine) OR vaccination) OR immunization) OR immune 191 response) OR antibodies))) AND (((((BMI) OR body mass index) OR quetelet index)) OR ((obesity) OR overweight)) #6 Search ((((hepatitis B) NOT mice) NOT rats)) AND (((((vaccine) OR vaccination) OR immunization) OR immune response) OR antibodies) #5 Search ((((BMI) OR body mass index) OR quetelet index)) OR ((obesity) OR overweight) #4 Search ((((vaccine) OR vaccination) OR immunization) OR immune response) OR antibodies #3 Search ((hepatitis B) NOT mice) NOT rats #2 Search ((BMI) OR body mass index) OR quetelet index #1 Search (obesity) OR overweight Cochrane Library #1 obesity or overweight (Word variations have been searched) #2 BMI or body mass index or quetelet index (Word variations have been searched) #3 hepatitis B not mice:ti,ab,kw not rats:ti,ab,kw (Word variations have been searched) 7799 #4 vaccine or vaccination or immunization or immune response or antibodies (Word variations have been searched) #5 #1 or # #6 #3 and # #7 #5 and #6 142 #8 MeSH descriptor: [Obesity] explode all trees

10 #9 MeSH descriptor: [Overweight] explode all trees 8661 #10 MeSH descriptor: [Body Mass Index] explode all trees 6280 #11 MeSH descriptor: [Hepatitis B Vaccines] explode all trees 817 #12 #8 or #9 or # #13 #12 and #11 5 #14 #7 or # Appendix 3 Inclusion-exclusion criteria Criteria Included Excluded Memo Basic information about papers searched Does the study on the effect of obesity on immunologic response to hepatitis B vaccine? If it does, whether the paper has a relevant topic on the questioned we are discussing? Yes Was the full-text available to be retrieved? Yes Was the paper written in English? Yes Types of participants Were they apparently healthy participants, with intact immune status, without previous HBV infection? Yes Were they in pregnant? Women only. Yes Were they free of predisposing factors for immunodeficiency? Like HIV/HCV co-infections, hemodialysis or any other diseases. Yes Was obesity measured by body mass index (BMI)? The cut-off points should be recorded in the Memo column. Yes Have the participants already received an at least 2-dose schedule of hepatitis B vaccine? Yes Types of vaccines Did the study use the recombinant vaccines? If not, record the details about the vaccine used in the study (such as combination vaccine, plasma-derived vaccine etc.) Yes Was the vaccination history clear?( for those without any Yes 9

11 details about the vaccination, and the type of vaccine used must be reported) Primary outcomes Was the successful immune response to hepatitis B vaccine defined as anti-hbs 10 IU/L? Yes Appendix 4 Data collection and abstraction form Row Data Results 1 1st author 2 Date of publication 3 Design of study 4 Type of vaccines used in the study 5 Type of the participants HCW General population (adults, aged 18 or older) Children/adolescents infants Mixed (need detailed description) 6 Country 7 Dose of injection conducted 8 Details about the schedule of vaccination, along with the number of doses 9 Route of injection 10 Area of injection 11 Needle length 12 Testing time interval (Since last dose) 13 Cut-off points of BMI 14 Booster use Yes (for non-responders) 15 Age range (the youngest and oldest age) 16 Sex ratio Item are to evaluated non-responsiveness to hepatitis B vaccine in obesity using the categorical data. Item are used to calculate unadjusted estimates (odds ratio, OR and 95% CI) 17 NO. of responders in the population without obesity. 18 NO. of non-responders in the population without obesity. 19 NO. of responders in the population with obesity. 20 NO. of non-responders in the population with obesity. Item are used to record adjusted estimates (if available) 21 Estimates for the effectiveness of hepatitis B vaccine in the obese compared to the non-obese. 22 upper limit of 95% CI of the adjusted estimates mentioned above 23 lower limit of 95% CI of the adjusted estimates mentioned above *** Basic judgment about either of the categorical or continuous data (whether available or not; whether can be used or not) 10

12 Appendix 5 The Agency for Healthcare Research and Quality (AHRQ) evaluation standard used for cross-sectional studies Item Yes Unclear 1) Define the source of information (survey, record review). 2) List inclusion and exclusion criteria for obese and non-obese subjects (cases and controls) or refer to previous publications. 3) Indicate time period used for identifying patients. 4) Indicate whether or not subjects were consecutive if not population-based. (If it is a population-based study, place a Yes. 5) Indicate if evaluators of subjective components of study were masked to other aspects of the status of the participants. 6) Describe any assessments undertaken for quality assurance purposes (e.g., test/retest of primary outcome measurements). 7) Explain any patient exclusions from analysis. 8) Describe how confounding was assessed and/or controlled. 9) If applicable, explain how missing data were handled in the analysis. (If no missing data exists, place a Yes in the blank.) 10) Summarize patient (non-responders) response rates and completeness of data collection 11) Clarify what follow-up, if any, was expected and the percentage of patients (non-responders) for which incomplete data or follow-up was obtained. Appendix 6 Check List for Quality Assessment and Scoring of Cohort Studies Check List Selection 1. Representativeness of the exposed cohort: Truly or somewhat representative of the general population following recombinant hepatitis B vaccine? (if yes, one star for subjects without obviously tendencies of becoming either obesity or non-obesity and not limited to either single gender) 2. Selection of the non-exposed cohort: whether the non-obese individuals were drawn from the same community as the exposed cohort did (if yes, one star for subjects without obviously tendencies of becoming either obesity or non-obesity and not limited to either single gender; no star if the subjects were ineligible or the selection of group was not described) 3. How was the exposure (obesity) ascertained in the cohort (if secure record and structured interview were applied, one star; no star if reports were written by participants themselves or relevant information was not described) Comparability 4. Group comparable for 1, 2, 3, 4 (if yes, one star; no star was assigned if the two groups differed in these characteristics or certain information was not given in the paper) 5. Group comparable for 5, 6 (if yes, one stars; no star was assigned if one of these three characteristics was different between the two groups or not reported) Outcome assessment 6. Clearly defined outcome of interest (yes, one star for information ascertained by using independent blind assessment or record linkage; no star if relevant information was not reported) 7. enough time of period for outcomes to occur (yes if the follow-up lasted at least 1 month (or 4 weeks) after the last dose of vaccination; no star if the time of period was not reached to) 8. Adequacy of follow-up (one star if follow-up 85%) Comparability variables: 1) age (either belongs to children/adolescents or adults); 2) dose; 3) route of administration; 4) 11

13 schedule; 5) booster (if same conditions were applied for non-responders in different groups); 6) testing time since the last dose of vaccination. Appendix 7 The Cochrane Collaboration s tool for assessing risk of bias Domain Support for judgement Review authors judgement Selection bias. Random sequence generation. Allocation concealment. Performance bias. Blinding of participants and personnel Assessments should be made for each main outcome (or class of outcomes). Detection bias. Blinding of outcome assessment Assessments should be made for each main outcome (or class of outcomes). Attrition bias. Incomplete outcome data Assessments should be made for each main outcome (or class of outcomes). Describe the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it should produce comparable groups. Describe the method used to conceal the allocation sequence in sufficient detail to determine whether intervention allocations could have been foreseen in advance of, or during, enrolment. Describe all measures used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. Provide any information relating to whether the intended blinding was effective. (Reported double blind fashion will also be considered as low-risk bias.) Describe all measures used, if any, to blind outcome assessors from knowledge of which intervention a participant received. Provide any information relating to whether the intended blinding was effective. Describe the completeness of outcome data for each main outcome, including attrition and exclusions from the analysis. State whether attrition and exclusions were reported, the numbers in each intervention group (compared with total randomized participants), reasons for attrition/exclusions where reported, and any re-inclusions in analyses performed by the review authors. (A 10% of missing values is acceptable for the low-risk bias assessment if the difference of completion rate in two groups were not reported.) Selection bias (biased allocation to interventions) due to inadequate generation of a randomised sequence. Selection bias (biased allocation to interventions) due to inadequate concealment of allocations prior to assignment. Performance bias due to knowledge of the allocated interventions by participants and personnel during the study. Detection bias due to knowledge of the allocated interventions by outcome assessors. Attrition bias due to amount, nature or handling of incomplete outcome data. Reporting bias. Selective reporting. State how the possibility of selective outcome reporting was examined by the review authors, and what was found. (The studies will be considered to be low risk if two types of outcomes are reported: (1) the overall seroprotection rate in the participants involved; (2) both seroprotection rates in obese group and non-obese group) Reporting bias due to selective outcome reporting. 12