***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND Recruitment , enrollment and retention of volunteers in an HIV vaccine trial is important in the efforts to ultimately develop a vaccine that can prevent new HIV infections . Following recruitment , some r and omized individuals decline to be enrolled in an HIV vaccine trial . The reasons for such a decision are not well known . This article describes why individuals who were r and omized in a phase I and II HIV vaccine trial in Dar es Salaam , Tanzania declined to be enrolled . METHODS Face-to-face interviews were conducted with 14 individuals ( 7 men and 7 women ) . Repeated readings of the 14 interview transcripts to look for reasons for declining to enroll in the trial were performed . Data was analyzed using the content analysis approach . RESULTS Informants expressed fear of the outcome of an experimental HIV vaccine  in their lives . Unlike women , some men were concerned over the effect of the vaccine on their reproduction intentions . Women were concerned about the unknown effects of the vaccine in their bodies . Also , to a large extent , informants faced resistance from significant others such as fiancées , parents , relatives , and friends . Women were influenced by their potential intimate sexual partners ; men were forbidden by their parents , and mothers had the most influential opinion . CONCLUSIONS Fear of the negative outcome of an experimental vaccine and resistance from significant others are the main reasons for declining to enroll in the HIV vaccine trial among eligible volunteers after r and omization . The resistance from the significant others provides valuable guidance for design ing future trials in Tanzania ; for example , exp and ing the HIV vaccine trial education to the general population from the onset of the trial design Behavioral and social issues were investigated in phase I/II preventive HIV vaccine trial volunteers in Thail and . These included risk behavior , HIV knowledge , distress , and social experiences associated with trial participation . Data were collected at baseline and at 4- and 8-month follow-up visits . Volunteers reported relatively low levels of risk behaviors at baseline and at the follow-up visits . About one fifth reported overtly negative reactions from family or friends . No problems with discrimination in employment , health care , or insurance were reported . Findings add to the evidence suggesting the feasibility of phase I/II prophylactic HIV vaccine trials with low-risk volunteers in Thail and Objectives : To assess the extent to which HIV‐negative cohort study participants would be willing to participate ( WTP ) in future HIV vaccine trials , to explore enrollment into an ongoing phase 3 HIV vaccine trial , and to assess changing WTP in such trials over time . Methods : The Vanguard Project is a prospect i ve study of gay and bisexual men in the greater Vancouver region , British Columbia , Canada .  Sociodemographic characteristics , sexual risk behavior , beliefs around HIV , and reasons for not participating in the  AIDSVAX B/B trial were collected from self‐administered question naires . Contingency table analysis compared subjects who were WTP with subjects who were not WTP . Logistic regression analyses identified possible predictors of WTP . A subset analysis was conducted to assess changes in WTP in 2001 versus 1997 . Results : Of 440 respondents , 214 ( 48.6 % ) were WTP , and 97 ( 22.0 % ) were not WTP . Those WTP were disadvantaged , sexually risky , and had a high‐perceived HIV risk ( all p < .05 ) . Reasons for not participating in the AIDSVAX B/B trial included fear of health problems and having missed the deadline for enrollment ( all p < 0.05 ) . Multivariate analysis revealed that having had a regular sex partner ( adjusted odds ratio , 0.48 [ confidence interval , 0.25‐0.92 ] ) was a negative predictor whereas having a high‐perceived HIV risk ( adjusted odds ratio , 5.35 [ confidence interval , 1.57‐18.25 ] ) was a positive predictor of WTP . Comparing WTP in 2001 with that in 1997 , 24 % of 100 participants who had been previously WTP were now not WTP . Conclusion : Improving community and participant knowledge about preventive HIV vaccine trials may help ensure informed consent . However , whether informing potential participants will reverse or contribute to the declining trend in WTP observed in this cohort warrants further investigation Objective : To determine the willingness of population s at high risk of HIV-1 infection to participate in HIV vaccine efficacy trials , determine factors influencing decision-making , and evaluate knowledge levels of vaccine trial concepts . Design : Cross-sectional study . Methods : HIV-1-negative homosexual men , male and female injecting drug users and non-injecting women at heterosexual risk were recruited in eight cities in the United States ( n = 4892 ) . Results : A substantial proportion of the study population ( 77 % ) would definitely ( 27 % ) or probably ( 50 % ) be willing to participate in a r and omized vaccine efficacy trial . Increased willingness was associated with high-risk behaviors , lower education level , being uninsured or covered by public insurance , and not having been in a previous vaccine preparedness study . Altruism and a desire for protection from the vaccine were major motivators for participation . Major concerns included positive HIV-1 antibody test due to vaccine , safety of the vaccine , and possible problems with insurance or foreign travel . Baseline knowledge of vaccine trial concepts was low . Conclusions : It is likely that high-risk volunteers will be willing to enroll in HIV vaccine efficacy trials . A variety of participant and community educational strategies are needed to address participant concerns , and to ensure underst and ing of key concepts prior to giving consent for participation The study objective was to assess willingness of men who have sex with men ( MSM ) enrollled in a vaccine preparedness study ( ' Projeto Rio ' ) to participate in phase III anti-HIV/AIDS vaccine trials . Overall , 57 % of Projeto Rio participants stated they would participate in a putative vaccine trial . MSM who reported commercial sex work were significantly ( p<0.05 ) more likely to engage in risky behaviours than others . In bivariate analysis , commercial sex workers ( CSWs ) were significantly ( p<0.05 ) more likely than non-commercial sex workers ( NCSWs ) to be willing to participate in vaccine trials ( 62.6 % versus 51.4 % ) . Among those willing , CSWs reported significantly more often ( p<0.05 ) ( 50.5 % ) than NCSWs ( 38.0 % ) that they would enroll to protect themselves from HIV . In multivariate analyses , variables associated with willingness to participate ( WTP ) were lower educational level , positive serology for syphilis , and ' engagement , under the influence of alcohol , in risky sexual practice s that would normally be avoided ' , but not commercial sex work . The potential enrollment in vaccine trials of MSM CWSs , as well as participants of low socio-economic status and high risk , seems thus to be possible Background To explore adolescent HIV risk perception , HIV vaccine knowledge , willingness to participate in future HIV vaccine clinical trials , and the factors that influence willingness to participate among high school students in Soweto , South Africa , we recruited school-going youth through r and omly selected local high schools . All pupils within the selected schools from whom parental consent and child assent could be obtained were eligible for participation . A self-administered , facilitated question naire was completed by all participants . Findings Perception of adolescent HIV risk was high . Some misconceptions regarding vaccine research were common , particularly regarding placebo and potential eligibility criteria for prophylactic vaccine trials . Of 240 responses to the willingness item , 84 ( 35 % ) indicated they were " probably willing " and 126 ( 52.5 % ) that they were " definitely willing to participate " . There were no significant differences in willingness by gender , age , school grade , or institution . Factors that were rated as " very important " in determining willingness included receiving current information about HIV research [ n = 201 ( 88.9 % ) ] , doing something to honour people who have HIV or have died of AIDS [ n = 168 ( 70.9 % ) ] , getting free counselling and testing [ n = 167 ( 70.5 ) ] , that participants may receive some protection against HIV infection from the vaccine [ n = 160 ( 70.2 % ) ] , and improving motivation to avoid risky behaviour [ n = 134 ( 59 % ) ] . ConclusionS oweto school-going youth report high degrees of willingness to participate in HIV vaccine trials . This may be related to the high levels of adolescent HIV risk perception . Whether hypothetical willingness translates to participation will await data from adolescent HIV vaccine trials The Underst and ing of volunteers in vaccine trials about their role as study participants and their voluntary commitment during the study are always one of the important concerns apart from evaluation of safety and efficacy of vaccine trials , especially in HIV prophylactic vaccine trials . The apprehension of indirectly risky behavior encouragement and deviated expectations among volunteers should be of concern . The current prospect i ve cohort study aim ed to assess and monitor the changes of risk behaviors , attitude and expectations among 164 volunteers from 2 studies of different prophylactic HIV vaccines , the Chiron HIV Thai E gp 120/MF59 + /- the Chiron HIV SF52 gp120 and Aventis Pasteur Live Recombinant ALVAC HIV ( vCP1521 ) priming with VaxGen gp120B/E ( AIDSVAX B/E ) boosting .  113 males and 51 females with a mean age ( + /- SD ) of 28.82 + /- 7.97 years old were enrolled from October 1997 to December 1998 and February 2000 to April 2001 .  Education and risk reduction counseling were regularly performed at every visit and question naires about risk behaviors , knowledge , attitudes , social influences and expectations were asked at baseline , 4 months and 12 months . No change of potentially HIV transmission related risk behavior was observed during the studies . There was a statistically significant decrease of risk sexual practice s from the beginning of the trials ( 42.2 % vs 1 % , p < 0.0001 ) . While 35.2 per cent from 62.2 per cent of the volunteers at the beginning of the study continued sexual practice with an identified single sexual partner at the end of the study ( p < 0.0001 ) . All of the volunteers expressed the beneficial expectations as knowledge gain , social contribution , feelings of having gained merit and self- benefits from health check-ups Behavioral and social issues were investigated in 363 phase I/II preventive HIV-1 vaccine trial volunteers in Thail and . These issues included risk behavior , HIV knowledge , distress , and social consequences of vaccine trial participation . Data were collected at baseline and at 4- , 8- , and 12-month follow-up visits . Volunteers reported relatively low levels of risk behaviors at baseline and at follow-up . Overtly negative reactions from family or friends were reported by 5.9 % . No experiences of discrimination in employment , health care , or insurance were reported . Mean levels of distress were low throughout the trial , and HIV-related knowledge was high , although it was common to consider the possibility of HIV transmission through casual contact . Findings add to the evidence that preventive HIV vaccine trials are feasible in Thail and Successful recruitment and retention of HIV-uninfected at-risk participants are essential for HIV vaccine efficacy trials . A multicountry vaccine preparedness study was started in 2003 to assess enrollment and retention of HIV-negative high-risk participants and to assess their willingness to participate in future vaccine efficacy trials . HIV-negative high-risk adults were recruited in the Caribbean , in Southern Africa , and in Latin America , and were followed for 1 year . Participants included men who have sex with men , heterosexual men and women , and female sex workers . History of sexually transmitted infections and sexual risk behaviors were recorded with HIV testing at 0 , 6 , and 12 months , and willingness to participate in future vaccine trials was recorded at 0 and 12 months . Recruitment , retention , and willingness to participate in future trials were excellent at 3 of the 6 sites , with consistent declines in risk behaviors across cohorts over time . Although not powered to measure seroincidence , HIV seroincidence rates per 100 person-years ( 95 % confidence interval [ CI ] ) were as follows : 2.3 ( 95 % CI : 0.3 to 8.2 ) in Botswana , 0.5 ( 95 % CI : 0 to 2.9 ) in the Dominican Republic , and 3.1 ( 95 % CI : 1.1 to 6.8 ) in Peru . The HIV Vaccine Trials Network 903 study helped to develop clinical trial site capacity , with a focus on recruitment and retention of high-risk women in the Americas , and improved network and site expertise about large-scale HIV vaccine efficacy trials Abstract There are few data on how the risk profiles of individuals who volunteer for HIV vaccine research  compare to the general population from which participants are recruited . This study contrasts demographic and sexual risk behaviours among volunteers in an HIV vaccine preparedness cohort with data from a cross-sectional community survey conducted in the same peri-urban community during the same time period . For the HIV vaccine preparedness cohort , structured question naires were administered to 140 HIV-negative individuals aged between 16 and 40 years . A question naire with identical measures was self-administer 
    Output:
    
Both the OECD and the non-OECD countries have similar barriers , and people 's decisions to participate in a clinical trial involve multiple barriers .