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Cognitive factors and willingness to participate in an HIV vaccine trial among HIV-positive injection… Dhalla, Shayesta; Poole, Gary; Singer, Joel; Patrick, David M.; Kerr, Thomas Jan 17, 2012

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Cognitive factors and willingness to participate in an HIVvaccine trial among HIV-positive injection drug usersShayesta Dhallaa, Gary Poolea, Joel Singera,b, David M. Patricka,c, and Thomas Kerrd,eaSchool of Population and Public Health, University of British Columbia, Vancouver, BritishColumbia, CanadabCanadian HIV Trials Network, Canadian HIV Trials Network, St. Paul’s Hospital, Vancouver, BC,CanadacBritish Columbia Centre for Disease Control, Vancouver, BC, CanadadBritish Columbia Centre for Excellence in HIV/AIDS, St. Paul’s Hospital, Vancouver, BC, CanadaeDivision of AIDS, Department of Medicine, University of British Columbia, Vancouver, BC,CanadaAbstractThere are gaps in our knowledge of the role cognitive factors play in determining people’swillingness to participate (WTP) in therapeutic HIV vaccine trials. Using a cross-sectional designin HIV-positive injection drug users (IDU), we determined the role of three cognitive factors: HIVtreatment optimism, self-efficacy beliefs, and knowledge of vaccine trial concepts in relation toWTP in a hypothetical phase 3 therapeutic HIV vaccine trial. Willingness to participate was 54%.Participants tended to be low in HIV treatment optimism (mean = 3.9/10), high in self-efficacy(mean = 79.8/100), and low in knowledge (mean = 4.1/10). Items pertaining to HIV treatmentoptimism and knowledge of HIV vaccine trial concepts were generally unrelated to WTP. Anincrease in self-efficacy had a statistically significant positive association with WTP (OR = 1.61,95% CI = 1.04–2.46, p<0.05). Furthermore, most of these HIV-positive participants had highlevels of self-efficacy, so we are most confident about this relationship at such levels.INTRODUCTIONCurrently, there is a need for the development and implementation of both a therapeutic andprophylactic HIV vaccine (Perrin, 2002). Therapeutic vaccination has been investigated withthe aim to increase immune responses in order to delay or reduce highly active antiretroviraltherapy use (HAART) and prevent disease development (Puls & Emery, 2006).At present, there is no licensed therapeutic vaccine for HIV. Only one phase 3 therapeuticHIV vaccine trial (Study 806) has been conducted in 77 centers in the United States (US)using the Salk HIV-1 immunogen (Remune) in the presence of antiretroviral therapy (ART)or no ART (Kahn, Cherng, Mayer, Murray, & Lagakos, 2000). This trial was unsuccessfulwith respect to HIV progression-free survival and overall mortality.A recently conducted therapeutic HIV vaccine phase 2 study in HIV-positive individualsincorporated a psychological substudy as part of a 3-arm trial (ALVAC+Remune vs.ALVAC alone vs. placebo) (Balfour et al., 2010). A goal of the substudy was to examine*Correspondence and reprint requests to: Dr. Shayesta Dhalla, 214 – 5550 Cambie Street, Vancouver, British Columbia, Canada, V6T1Z3, Tel: 1-604-321-4116, shayestadhalla@yahoo.com.NIH Public AccessAuthor ManuscriptPsychol Health Med. Author manuscript; available in PMC 2013 March 01.Published in final edited form as:Psychol Health Med. 2012 ; 17(2): 223–234. doi:10.1080/13548506.2011.608803.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptHIV patients’ baseline motivation for participating in a therapeutic HIV vaccine trial using arisk/benefit analysis. It was found that patients enrolled in the trial felt that potential socialand personal benefits of participating outweighed potential social and personal risks. Forexample, 81% of people felt that participating in an HIV vaccine trial was a way to honorpeople who died of AIDS, while 69% cited side effects and 34% cited future healthproblems as potential risks.More vaccine research is needed in HIV-positive individuals, and their willingness toparticipate (WTP) in such research must be better understood. Cognitive factors can beexamined as predictors of WTP in an HIV vaccine trial, and the present study focused onsuch factors, including HIV treatment optimism, self-efficacy beliefs, and knowledge ofHIV vaccine concepts. To our knowledge, these cognitive factors have not previously beenexamined in the context of a therapeutic HIV vaccine preparedness study (VPS), specificallyin injection drug users (IDU).Cognitive factorsOptimism has been defined as the “hopefulness and confidence about the future or thesuccess of something” (Soanes & Stevenson, 2005). Optimism in the context of atherapeutic trial would be important to examine as HIV treatment optimism (hopefulnessand confidence in the success of treatment, e.g., HAART) may potentially be associatedwith high or low vaccine/vaccine trial optimism.Self-efficacy is concerned not with the existence of specific skills, but with the one’sjudgements about what one can do with those skills (Bandura, 1986). Self-efficacy isimportant because a person’s belief that he/she can comply and adhere to a protocol could beimportant in a multi-dose regimen vaccine trial. To our knowledge, there has been no self-efficacy scale developed in IDU for an HIV vaccine trial.Knowledge is defined as the “information and understanding of a specific topic or of theworld in general, usually acquired by experience or by learning” (Vandenbos, 2007).Knowledge is ethically necessary for informed consent and may be associated with WTP ina vaccine trial. Various knowledge scales exist for these purposes (Koblin et al., 1998;Koblin, Holte, Lenderking, & Heagerty, 2000; Smit, Middelkoop, Myer, Seedat, Bekker, &Stein, 2006; Starace, Wagner, Luzi, Cafaro, Gallo, & Rezza, 2006).Objectives and HypothesesThe present study examines the relationship between selected cognitive factors and WTP ina hypothetical HIV therapeutic vaccine trial in IDU in the Downtown Eastside ofVancouver, Canada. We sought to determine the effects of HIV treatment optimism, self-efficacy regarding a vaccine trial, and knowledge of HIV vaccine trial concepts in relation toWTP in an HIV vaccine trial. We also examined the effects of sociodemographic variables,drug use and risk behaviors, measures of health service utilization, and psychosocial factorsin relation to WTP. We hypothesized that higher self-efficacy would be positively related toa greater WTP. We also hypothesized that treatment optimism and knowledge would beassociated with WTP, though we could not predict the direction of this relationship.METHODSProcedureParticipants in the present cross-sectional study were IDU who were also part of the AIDSCare Cohort to Evaluate Exposure to Survival Services study (ACCESS), a prospectivecohort study in HIV-positive IDU that began in December 2005. A detailed description ofDhalla et al. Page 2Psychol Health Med. Author manuscript; available in PMC 2013 March 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author Manuscriptthis cohort is provided elsewhere (Uhlmann et al., 2010). Participants completed aninterviewer-administered questionnaire collecting demographic data, information aboutrecent drug use patterns, HIV risk behaviors, and experiences in addiction treatment.Participants were reimbursed $20 Canadian (CDN) dollars for the study visit, at which timereferrals were provided for universal medical care, HIV/AIDS care, and available drug andalcohol treatment. The study has been approved on an annual basis by the Providence HealthCare/University of British Columbia (UBC) Research Ethics Board.Data collection for the present study took place within the larger context of the ACCESSstudy. A sample size of 85 participants was made available. Notably, a similar study with alarger sample size of 276 HIV-negative participants yielded close to equivalent results forthe cognitive factor data in relation to WTP (Dhalla et al., 2010).Presentation of informationAfter the conclusion of the main ACCESS study questionnaire, trained interviewersadministered eight items pertaining to knowledge of HIV vaccine trial concepts (withpermission, Koblin, November 2007) (Koblin et al., 2000) (Appendix 1). These itemsfocused on concepts such as randomization, blinding, placebos, safety, adverse reactions,and vaccine-induced seropositivity. If participants did not know what a vaccine was, thedefinition was explained by the interviewer. Previous work in this area presented theprospect of vaccine trials as being likely without giving respondents the impression that theywere being invited to a specific trial and our script was written to be consistent with thisprecedent (Koblin et al., 2000).Measurement scalesAs part of the larger interview, trained interviewers administered three measurement scalesaddressing HIV treatment optimism (2 items) (Table 1), self-efficacy (5 items) (Appendix 1[SQ1]), and knowledge of vaccine trial concepts (10 true/false items) (Table 1, Appendix 1[SQ2]). The HIV treatment optimism items were already part of the main ACCESS studyquestionnaire.Appendix 1 shows the order of items presented to participants after the main ACCESS studyquestionnaire.In terms of validation of the optimism scale, Van De Ven et al. (2000) developed a 12-itemtreatment optimism scale in gay men (15.2% reported they were HIV-positive) which wasshown to have predictive validity and generalizability (Van de Ven, Crawford, Kippax,Knox, & Prestage, 2000). For the present study, the two HIV treatment optimism items,similar to those used by Van de Ven et al. (2000), were summed to obtain an HIV treatmentoptimism total score (Table 1).The self-efficacy scale was a supplemental scale administered after the conclusion of themain ACCESS study questionnaire (Appendix 1 [SQ1]). The self-efficacy items were basedon a previous self-efficacy scale in HIV-positive individuals that had predictive validity forHAART continuation and high internal consistency (α = 0.82) (Kerr et al., 2005). In thepresent study, composite self-efficacy scores were calculated by adding the subscale scoresand dividing the sum by the total number of subscale items (Kerr et al., 2005).The knowledge scale was also a supplemental scale administered after the conclusion of themain ACCESS study questionnaire (Appendix 1 [SQ2]). The 10 knowledge true/false itemswere taken from a study in HIV-negative individuals (Halpern, Metzger, Berlin, & Ubel,2001; Koblin et al., 2000) (with permission, Koblin, November 2007), although the scalehas knowledge items also pertaining to preventive trials. The scale was kept intact to allowDhalla et al. Page 3Psychol Health Med. Author manuscript; available in PMC 2013 March 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author Manuscriptfor comparison to other studies such as ours administering the scale to HIV-negativeindividuals (Dhalla et al., 2010). The knowledge questions were categorized as correct vs.incorrect/do not know. Corrected item-total correlations for the knowledge items were alsocalculated.Outcome variableWillingness to participate was the outcome variable and was assessed via the question: “Ifan HIV vaccine study were available, would you be willing to participate in it?” (Appendix1 [SQ0]). Five possible answers were provided: “definitely not ”, “probably not”, “don’tknow”, “probably ”, and “definitely”. The outcome variable was dichotomized into“definitely/probably” vs. “definitely not/probably not”. Those who answered “don’t know”for WTP were excluded from the analysis.Statistical AnalysisData analysis was undertaken using SPSS Version 17.0. Contingency table analysis wasused to compare willing with unwilling subjects (Table 1). The t-test was used for normallydistributed continuous variables, while the Mann-Whitney test was used for skewedcontinuous variables. The p-value of self-efficacy (p ≤ 0.07, 1-tailed test) was the criterionfor variable inclusion in a logistic regression model, as self-efficacy was the primaryvariable that we chose to examine in the present study.RESULTSBetween June 2007 and May 2008, 85 HIV-positive individuals were recruited forparticipation in this study. The number of people who were “definitely willing” toparticipate was 24 (28%), “probably willing” was 22 (26%), “probably not willing” was 15(18%), and “definitely not willing” was 14 (17%). Ten people (12%) responded “don’tknow”, leaving 75 participants for our analysis. Overall, 54% of individuals were WTP. Forthe sample analyzed, 57% were male and 48% were of Aboriginal ethnicity, and 65% wereon HAART. The follow-up rate in the ACCESS participants was 82% during the period of2007–2008. This value can be linked to self-efficacy in that these participants could believethat they could follow up in an actual HIV vaccine trial.HIV treatment optimismParticipants tended to be low in HIV treatment optimism (most values < 3/10). The meanHIV treatment optimism score was 3.9/10. The Mann-Whitney test showed that the HIVtreatment optimism sum was not significantly related to WTP (p = 0.95). As well, the HIVtreatment optimism sum was unrelated to Aboriginal ethnicity (p = 0.44) and sex (p = 0.12).The correlation between the two HIV treatment optimism items was 0.49.Self-efficacyParticipants tended to be high in self-efficacy (most values >80/100). The mean self-efficacyscore was 79.8/100. In a logistic regression analysis, a 20-unit increase in self-efficacy wassignificantly and positively associated with WTP (odds ratio [OR] = 1.61, 95% CI = 1.04–2.46, p<0.05). The self-efficacy items were highly correlated with each other (range = 0.44to 0.92) and Cronbach’s α was 0.89, indicating high internal consistency. Scores above 0.7are the usual criteria for adequate internal consistency (Horne et al., 2004). The sum ofefficacy expectations items #1 to #4 in our self-efficacy scale yielded a self-efficacy meanvalue of 85.1 for WTP, and 72.0 for not WTP. These are similar values to the mean valuesof efficacy expectations in the study by Kerr et al (2005), which showed the mean values tobe 87.6 for no HAART discontinuation, and 70.5 for HAART discontinuation.Dhalla et al. Page 4Psychol Health Med. Author manuscript; available in PMC 2013 March 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptKnowledge of HIV vaccine trial conceptsParticipants tended to be low in this knowledge with a mean knowledge score of 4.1/10. Ingeneral, the knowledge items were unrelated to WTP. The sum of the 10 knowledge itemswas unrelated to WTP in a therapeutic HIV vaccine trial (Table 1). As knowledge items #1to #4 (Table 2) pertained more specifically to preventive HIV vaccine trials, rather thantherapeutic HIV vaccine trials, a separate subanalysis was conducted and showed that thesum of knowledge items #5 to #10 (Table 2) was also unrelated to WTP in a therapeuticHIV vaccine trial.In light of the STEP study results, we paid particular attention to knowledge item #7, whichstated “Once a large-scale HIV vaccine trial begins, we can be sure the vaccine iscompletely safe” (correct answer = false). This item was responded to correctly by only 35%of participants. The STEP study showed greater HIV acquisition in the group vaccinatedwith an adenovirus type 5 (Ad5) vaccine, who had pre-existing immunity to Ad5, comparedto a placebo amongst uncircumcised men (Gray, Buchbinder, & Duerr, 2010). This resultbrought into question the issue of safety of the Ad5 vaccine and any future vaccines.Cronbach’s alpha was 0.64 for the knowledge items, slightly higher than in our study inHIV-negative individuals (alpha = 0.61) (Dhalla et al., 2010). Corrected item-totalcorrelations showed several items below a recognized cut-off of 0.3, indicating lowcorrelation with the overall scale (Table 2) (Field, 2009).Being on HAART treatment was not significantly related to WTP in a therapeutic HIVvaccine trial (p = 0.60) or to HIV treatment optimism (Mann-Whitney = 0.25). As well,removing the variable on daily crack use from the analysis did not result in a significantchange in the relationship between self-efficacy and WTP.DISCUSSIONTo our knowledge, this is among the first therapeutic phase 3 HIV VPS conducted todetermine factors associated with WTP in a hypothetical HIV vaccine trial in IDU.Willingness to participate was found to be 54%. A 20-unit increase in self-efficacy wassignificantly and positively related to WTP (OR = 1.61, 95% CI = 1.04–2.46, p<0.05). HIVtreatment optimism, and the knowledge sum were unrelated to WTP. These results aresimilar to our recent VPS in HIV-negative individuals (Dhalla et al., 2010).We were unable to identify a previous study examining the relationship between HIVtreatment optimism and WTP in an HIV vaccine trial, in HIV-positive individuals. However,in a previous study in a Swedish general population, it was found that optimism surroundingan HIV vaccine developed in the next 5 years was positively related to the belief thattreatment with HAART reduced infectivity (Herlitz & Steel, 2001). Further studies could bedeveloped to discover the important relationship specifically between vaccine optimism andWTP, as well as the longitudinal relationship between optimism and sexual behavior.Given previous findings (Kerr et al., 2005), it is reasonable that self-efficacy may factor intodecisions such as WTP. Therefore, from our study, high self-efficacy scores may be usefulin the enrolment of individuals into a phase 3 therapeutic HIV vaccine trial. However, asthere was a lack of data at lower values of self-efficacy, the relationship between self-efficacy and WTP at lower levels of self-efficacy was inconclusive. Cognitive-behavioralinterventions could be used to increase self-efficacy, potentially increasing WTP (Barclay etal., 2007). For example, it could be explained to participants that as they are able to follow-up in the ACCESS study, they would in effect be capable of following up in an actual HIVvaccine trial.Dhalla et al. Page 5Psychol Health Med. Author manuscript; available in PMC 2013 March 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptKnowledge item #7 (see Table 2), which assessed HIV vaccine safety (Koblin et al., 2000)could also be asked more specifically with respect to the STEP study results (von Bubnoff &Jeffreys, 2009). A recent study by Newman et al. (2008) in Toronto, Canada, found thatconcerns about vaccine safety were associated with uncertainty in WTP with respect to thephase 2B STEP study, though the respondents in Toronto were mainly gay men.The knowledge scale in our study had a Cronbach’s α = 0.64, indicating the scale could befurther refined, or other more reliable knowledge scales could be used (Smit, Middelkoop,Myer, Seedat, Bekker, & Stein, 2006). In previous studies by Koblin et al. who developedthe knowledge scale used in the present study, internal consistency was not reported (Koblinet al., 2000). Knowledge in relation to WTP in IDU has yielded contradictory results inseparate studies also using Koblin’s scale (Halpern et al., 2001; Koblin et al., 2000). Otherstudies have used various knowledge scales in IDU (Harrison, Vlahov, Jones, Charron, &Clements, 1995) and other populations (Smit, Middelkoop, Myer, Seedat, Bekker, & Stein,2006; Starace, Wagner, Luzi, Cafaro, Gallo, & Rezza, 2006). Koblin et al. (1998) developedanother similar scale than used in the present study, although the scale consisted of moreitems. The original purpose of the knowledge scales was to ensure that participantsunderstood all the relevant study information, and that their consent was truly informed.A large percentage (65%) of the ACCESS cohort claimed they were on HAART treatment,but in our analysis, being on treatment did not affect their WTP. Treatment with HAART isnot without complications such as toxicities and necessity for long-term adherence(Thompson et al., 2010). Given this, potential participants may be duly concerned about theshort-term and long-term side effects of adding another medical intervention in the form ofan HIV therapeutic vaccine.In reference to WTP, it should be noted that the progression to development of AIDS maypotentially be a concern to these HIV-positive individuals, but this may be offset by the factthat many participants were already on HAART. The discouraging results of the STEP study(von Bubnoff & Jeffreys, 2009) may also negatively affect WTP, although the STEP studywas in HIV-negative individuals. Only 35% of individuals were aware that there may beissues surrounding vaccine safety in general, and this suggests that individuals should beeducated prior to conducting a therapeutic HIV vaccine trial in this case.Previous studies have examined HIV vaccine acceptability (Newman & Logie, 2010).However, the concept of vaccine acceptability refers to taking a proven vaccine, while WTPin the present instance refers to participation in an HIV vaccine trial that utilizes anunproven vaccine (therefore WTP may be lower). Determinants of participation includingself-efficacy and altruism may differ depending on whether one is examining vaccineacceptability versus WTP in a vaccine trial.LimitationsThere were several limitations in our study. The ACCESS cohort is a non-random sampleand only a small subsample of the cohort was included in this particular study. These issuescould affect generalizability and increase the likelihood of a Type 2 error. Another issue isthat the study could not examine changes in cognitive factors over time. Furthermore, oralinterviews might have resulted in socially desirable reporting. Another limitation of ourstudy was that the order of scale administration was not varied between participants.Furthermore, treatment optimism may also not necessarily be a proxy for vaccine optimism.In addition, there were only two items in the treatment optimism scale, and more itemswould be required to improve scale reliability. As well, it is possible that the answers onknowledge were not based on true understanding of vaccine trial concepts but on rote recall.Another limitation of the study was that some of the items on the knowledge scale were notDhalla et al. Page 6Psychol Health Med. Author manuscript; available in PMC 2013 March 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author Manuscriptapplicable to therapeutic HIV vaccine trials. The psychometrics of Koblin’s scale (2000)were also not strong (alpha = 0.64). It should also be kept in mind that trials at specific sitesdepend on local cultural and social environments (Lau, Stansbury, Gust, & Kafaar, 2009).CONCLUSIONSThis study addresses gaps in knowledge regarding cognitive factors and WTP in therapeuticHIV vaccine trials. In this study, HIV treatment optimism and knowledge of vaccine trialconcepts were unrelated to WTP in a therapeutic HIV vaccine trial. At higher values, self-efficacy may be useful in increasing WTP in a therapeutic HIV vaccine trial. The self-efficacy scale that we have developed may be validated to determine the relationship toWTP in other populations and settings. A prediction model could be developed to quantifythe contribution of self-efficacy to variations in WTP. To build on a recent study whichexamined factors associated with non-enrolment in the phase 2B STEP study (Newman etal., 2008), quantitative (e.g., Likert-type scales) and qualitative (e.g., focus groups) researchin IDU could further examine WTP in an HIV vaccine trial, as well as knowledge andbeliefs surrounding vaccine trial concepts in IDU. The knowledge scale used in the presentstudy could be further refined for future HIV vaccine trials.Supplementary MaterialRefer to Web version on PubMed Central for supplementary material.AcknowledgmentsThe authors would like to thank Dr. Robert Hogg who contributed to the topic of the study. They would also like toacknowledge Dr. Evan Wood, who is the principal investigator of the AIDS Care Cohort to Evaluate Exposure toSurvival Services Study (ACCESS) and was involved in day to day management of the cohort during the periodthat data for the present study were collected. They would also like to thank Dr. Jonathon Angel for his contributionto the Introduction section of our manuscript; Dr. Chris Richardson, who provided advice on data analysis; and Dr.Hubert Wong, who assisted in data interpretation.The authors would like to acknowledge the study participants for their contribution to the research, as well ascurrent and past researchers and staff. They would specifically like to thank Deborah Graham, Tricia Collingham,Caitlin Johnston, Steve Kain, Kathy Li, and Calvin Lai for their research and administrative assistance. 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[PubMed: 16336205]Smit J, Middelkoop K, Myer L, Seedat S, Bekker LG, Stein DJ. Willingness to participate in HIVvaccine research in a peri-urban South African community. International Journal of STD & AIDS.2006; 17(3):176–179. [PubMed: 16510005]Soanes, C.; Stevenson, A., editors. The Oxford Dictionary of English. Oxford: Oxford UniversityPress; 2005. (revised ed.)Starace F, Wagner TM, Luzi AM, Cafaro L, Gallo P, Rezza G. Knowledge and attitudes regardingpreventative HIV vaccine clinical trials in Italy: Results of a national survey. AIDS Care. 2006;18(1):66–72. [PubMed: 16282079]Thompson MA, Aberg JA, Cahn P, Montaner JS, Rizzardini G, Telenti A, et al. Antiretroviraltreatment of adult HIV infection:2010 recommendations of the International AIDS Society-USApanel. Journal of the American Medical Association. 2010; 304(3):321–333. [PubMed: 20639566]Dhalla et al. Page 8Psychol Health Med. Author manuscript; available in PMC 2013 March 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptUhlmann S, Milloy MJ, Kerr T, Zhang R, Guillemi S, Marsh D, et al. Methadone maintenance therapypromotes initiation of antiretroviral therapy among injection drug users. Addiction. 2010; 105(5):907–913. [PubMed: 20331553]Van de Ven P, Crawford J, Kippax S, Knox S, Prestage G. A scale of optimism-scepticism in thecontext of HIV treatments. AIDS Care. 2000; 12(2):171–176. [PubMed: 10827857]Vandenbos, GR. APA Dictionairy of Psychology. 1st ed.. American Psychological Association; 2007.von Bubnoff A, Jeffreys R. Capsules from Keystone. International AIDS Vaccine Initiative (IAVI)Report. 2009; 13:4–7. 14–16.Dhalla et al. Page 9Psychol Health Med. Author manuscript; available in PMC 2013 March 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptDhalla et al. Page 10Table 1Factors associated with willingness to participate in an HIV vaccine trial among HIV-positive injection drugusers (n=75)Variable WTP(n=46)n (%)not WTP(n=29)n (%)p-value*SociodemographicsAge mean (median)(IQR)**42.3 years (43.7)(35.6–48.0)41.7 years (43.1)(36.9–46.9) 0.76*(t-test)Female (reference)Male19 (41)27 (59)13 (45)16 (55)0.76Aboriginal ethnicity*** 20 (43) 16 (55) 0.32Education ≥ high school 24 (52) 13 (45) 0.54Employment 9 (20) 4 (14) 0.76¥Unstable Housing† 37 (80) 21 (72) 0.42Drug use & risk variablesBorrowed needles† 2 (4) 1 (3) 1.00¥Lent needles† 1 (2) 0 1.00¥Injection heroin ≥daily‡ 9 (20) 7 (24) 0.64Injection cocaine ≥ daily‡ 5 (11) 2 (7) 0.70¥Smoking crack ≥ daily‡ 25 (54) 9 (31) 0.05Sex trade involvement† 4 (9) 5 (17) 0.30¥Incarceration† 7 (15) 2 (7) 0.47¥Health Service and UtilizationAttended NEP (ever vs. never) 34 (74) 16 (55) 0.09NEP ≥ 1/week 17 (37) 10 (34) 0.83Injecting in Insite (ever vs. never 34 (74) 19 (66) 0.44Injecting in Insite† 24 (52) 13 (45) 0.54Drug / alcohol treatment† 23 (50) 15 (52) 0.88Psychosocial VariablesDepression (≥ 16)§(n = 62)26 (67)(n=39)14 (61)(n=23)0.65Cognitive FactorsTreatment optimismBy taking HIV medicines, an HIV+ person reduces the chance of infecting someone withHIV through sharing needles▪0.73By taking HIV medicines, an HIV+ person reduces the chance of infecting someone withHIV through unprotected sex▪0.74Treatment optimism sum 0.95Knowledge Questions Correct vs. Incorrect / Don’t know (Question)Psychol Health Med. Author manuscript; available in PMC 2013 March 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptDhalla et al. Page 11Variable WTP(n=46)n (%)not WTP(n=29)n (%)p-value*   1 12 (26) 10 (34) 0.44   2 11 (24) 8 (28) 0.72   3 16 (33) 13 (45) 0.38   4 24 (52) 16 (55) 0.80   5 4 (8) 9 (31) 0.03¥   6 25 (51) 12 (41) 0.28   7 13 (27) 13 (45) 0.14   8 17 (35) 13 (45) 0.50   9 18 (39) 13 (45) 0.63   10 39 (85) 19 (66) 0.05Knowledge sum (items 1–10) 0.41(t-test)HAART treatment 29 (63) 20 (69) 0.60Notes: NEP, needle-exchange program; HAART, highly active antiretroviral therapy.*Two-tailed probability.**IQR, Interquartile range***First Nations (native), Metis, or Inuit.†Activities in the last 6 months.‡Current activities.¥Fisher’s exact test.§Center for Epidemiologic Studies Depression Scale (CES-D) (20 item 4-point scale) standard cut-off score of ≥ 16.▪5-point optimism scale ranging from “strongly disagree” to “strongly agree”.Psychol Health Med. Author manuscript; available in PMC 2013 March 01.NIH-PA Author ManuscriptNIH-PA Author ManuscriptNIH-PA Author ManuscriptDhalla et al. Page 12Table 2Corrected item-total correlations of knowledge scale (n = 75)Knowledge item Corrected item-total correlation1. An HIV vaccine could weaken the immune system’s ability to fight off HIV infection 0.052. Only vaccines that are known to be at least 50% effective at preventing HIV will be tested 0.293. The vaccine will have no effect on a participant’s HIV test results 0.494. If people test HIV-positive after the vaccine, they may really be infected with HIV, or they may just be having areaction to the vaccine0.195. People in these studies will receive health care for any medical problems they have 0.146. People in a vaccine study will know whether or not they got the placebo because only the vaccine will cause sideeffects0.487. Once a large-scale HIV vaccine trial begins, we can be sure the vaccine is completely safe 0.308. People in these studies are guaranteed to be in any future vaccine studies 0.439. The study nurse will decide who gets the real vaccine and who gets placebo 0.4910. Some participants will get the real vaccine and some will get a placebo 0.22Psychol Health Med. Author manuscript; available in PMC 2013 March 01.

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