Disgust as an emotional driver of vaccine attitudes and uptake? A mediation analysis.

Research on the drivers of vaccine acceptance has expanded but most interventions fall short of coverage targets. We explored whether vaccine uptake is driven directly or indirectly by disgust with attitudes towards vaccines acting as a possible mediator. An online cross-sectional study of 1007 adults of the USA via Amazon's Mechanical Turk was conducted in January 2017. The questionnaire consisted of four sections: (1) items assessing attitudes towards vaccines and vaccine uptake, (2) revised Disgust Scale (DS-R) to measure Disgust Sensitivity, (3) Perceived Vulnerability to Disease scale (PVD) to measure Germ Aversion and Perceived Susceptibility, and (4) socio-demographic information. Using mediation analysis, we assess the direct, the indirect (through Vaccine Attitudes) and the total effect of Disgust Sensitivity, Germ Aversion and Perceived Susceptibility on 2016 self-reported flu vaccine uptake. Mediation analysis showed the effect of Disgust Sensitivity and Germ Aversion on vaccine uptake to be twofold: a direct positive effect on vaccine uptake and an indirect negative effect through Vaccine Attitudes. In contrast, Perceived Susceptibility was found to have only a direct positive effect on vaccine uptake. Nonetheless, these effects were attenuated and small compared to economic, logistic and psychological determinants of vaccine uptake.

On the origin and timing of Zika virus introduction in Brazil.

The timing and origin of Zika virus (ZIKV) introduction in Brazil has been the subject of controversy. Initially, it was assumed that the virus was introduced during the FIFA World Cup in June-July 2014. Then, it was speculated that ZIKV may have been introduced by athletes from French Polynesia (FP) who competed in a canoe race in Rio de Janeiro in August 2014. We attempted to apply mathematical models to determine the most likely time window of ZIKV introduction in Brazil. Given that the timing and origin of ZIKV introduction in Brazil may be a politically sensitive issue, its determination (or the provision of a plausible hypothesis) may help to prevent undeserved blame. We used a simple mathematical model to estimate the force of infection and the corresponding individual probability of being infected with ZIKV in FP. Taking into account the air travel volume from FP to Brazil between October 2013 and March 2014, we estimated the expected number of infected travellers arriving at Brazilian airports during that period. During the period between December 2013 and February 2014, 51 individuals travelled from FP airports to 11 Brazilian cities. Basing on the calculated force of ZIKV infection (the per capita rate of new infections per time unit) and risk of infection (probability of at least one new infection), we estimated that 18 (95% CI 12-22) individuals who arrived in seven of the evaluated cities were infected. When basic ZIKV reproduction numbers greater than one were assumed in the seven evaluated cities, ZIKV could have been introduced in any one of the cities. Based on the force of infection in FP, basic reproduction ZIKV number in selected Brazilian cities, and estimated travel volume, we concluded that ZIKV was most likely introduced and established in Brazil by infected travellers arriving from FP in the period between October 2013 and March 2014, which was prior to the two aforementioned sporting events.

Positive selection drives accelerated evolution of mosquito salivary genes associated with blood-feeding.

The saliva of bloodsucking animals contains dozens to hundreds of proteins that counteract their hosts' haemostasis, inflammation and immunity. It was previously observed that salivary proteins involved in haematophagy are much more divergent in their primary sequence than those of housekeeping function, when comparisons were made between closely related organisms. While this pattern of evolution could result from relaxed selection or drift, it could alternatively be the result of positive selection driven by the intense pressure of the host immune system. We investigated the polymorphism of five different genes associated with blood-feeding in the mosquito Anopheles gambiae and obtained evidence in four genes for sites with signatures of positive selection. These results add salivary gland genes from bloodsucking arthropods to the small list of genes driven by positive selection.

Global pharmacogenomics: Impact of population diversity on the distribution of polymorphisms in the CYP2C cluster among Brazilians.

The impact of biogeographical ancestry, self-reported 'race/color' and geographical origin on the frequency distribution of 10 CYP2C functional polymorphisms (CYP2C8*2, *3, *4, CYP2C9*2, *3, *5, *11, CYP2C19*2, *3 and *17) and their haplotypes was assessed in a representative cohort of the Brazilian population (n=1034). TaqMan assays were used for allele discrimination at each CYP2C locus investigated. Individual proportions of European, African and Amerindian biogeographical ancestry were estimated using a panel of insertion-deletion polymorphisms. Multinomial log-linear models were applied to infer the statistical association between the CYP2C alleles and haplotypes (response variables), and biogeographical ancestry, self-reported Color and geographical origin (explanatory variables). The results showed that CYP2C19*3, CYP2C9*5 and CYP2C9*11 were rare alleles (<1%), the frequency of other variants ranged from 3.4% (CYP2C8*4) to 17.3% (CYP2C19*17). Two distinct haplotype blocks were identified: block 1 consists of three single nucleotide polymorphisms (SNPs) (CYP2C19*17, CYP2C19*2 and CYP2C9*2) and block 2 of six SNPs (CYP2C9*11, CYP2C9*3, CYP2C9*5, CYP2C8*2, CYP2C8*4 and CYP2C8*3). Diplotype analysis generated 41 haplotypes, of which eight had frequencies greater than 1% and together accounted for 96.4% of the overall genetic diversity. The distribution of CYP2C8 and CYP2C9 (but not CYP2C19) alleles, and of CYP2C haplotypes was significantly associated with self-reported Color and with the individual proportions of European and African genetic ancestry, irrespective of Color self-identification. The individual odds of having alleles CYP2C8*2, CYP2C8*3, CYP2C9*2 and CYP2C9*3, and haplotypes including these alleles, varied continuously as the proportion of European ancestry increased. Collectively, these data strongly suggest that the intrinsic heterogeneity of the Brazilian population must be acknowledged in the design and interpretation of pharmacogenomic studies of the CYP2C cluster in order to avoid spurious conclusions based on improper matching of study cohorts. This conclusion extends to other polymorphic pharmacogenes among Brazilians, and most likely to other admixed populations of the Americas.

Impact of CYP4F2 rs2108622 on the stable warfarin dose in an admixed patient cohort.

There is controversy regarding the association between the CYP4F2 rs2108622 (V33M) polymorphism and warfarin dose requirement in white patients, and there are no data for nonwhite populations. We observed no association in self-identified white, black, or "intermediate" Brazilian patients (n = 370). The addition of the rs2108622 genotype as a variable has only a marginal effect on the predictive power of a warfarin dosing algorithm derived from this patient cohort. We conclude that prospective CYP4F2 genotyping is not justified in Brazilians who are potential candidates for warfarin therapy.

Impact of insecticide interventions on the abundance and resistance profile of Aedes aegypti.

Insecticide-based vector control is the primary strategy for curtailing dengue transmission. We used a mathematical model of the seasonal population dynamics of the dengue mosquito vector, Aedes aegypti, both to assess the effectiveness of insecticide interventions on reducing adult mosquito abundance and to predict evolutionary trajectories of insecticide resistance. We evaluated interventions that target larvae, adults, or both. We found that larval control and adult control using ultra-low-volume insecticide applications can reduce adult mosquito abundance with effectiveness that depends on the frequency of applications. We also found that year-long continuous larval control and adult control, using either insecticide treatment of surfaces and materials or lethal ovitraps, imposed the greatest selection for resistance. We demonstrated that combined targeting of larvae and adults at the start of the dengue season is optimal. This intervention contrasts with year-long continuous larval control policies adopted in settings in which dengue transmission occurs.

Pharmacogenetics of warfarin: development of a dosing algorithm for brazilian patients.

A dosing algorithm including genetic (VKORC1 and CYP2C9 genotypes) and nongenetic factors (age, weight, therapeutic indication, and cotreatment with amiodarone or simvastatin) explained 51% of the variance in stable weekly warfarin doses in 390 patients attending an anticoagulant clinic in a Brazilian public hospital. The VKORC1 3673G>A genotype was the most important predictor of warfarin dose, with a partial R(2) value of 23.9%. Replacing the VKORC1 3673G>A genotype with VKORC1 diplotype did not increase the algorithm's predictive power. We suggest that three other single-nucleotide polymorphisms (SNPs) (5808T>G, 6853G>C, and 9041G>A) that are in strong linkage disequilibrium (LD) with 3673G>A would be equally good predictors of the warfarin dose requirement. The algorithm's predictive power was similar across the self-identified "race/color" subsets. "Race/color" was not associated with stable warfarin dose in the multiple regression model, although the required warfarin dose was significantly lower (P = 0.006) in white (29 +/- 13 mg/week, n = 196) than in black patients (35 +/- 15 mg/week, n = 76).

Effectiveness of BCG vaccination among leprosy contacts: a cohort study.

The study assessed the effectiveness of BCG vaccination against leprosy among the contacts of 1161 leprosy patients at the FIOCRUZ Leprosy Outpatient Clinic, RJ, Brazil, from June 1987 to December 2006. Following National Leprosy Program guidelines, the clinic has administered one-to-two doses to all healthy contacts since 1991. Among the 5680 contacts, 304 (5.4%) already had leprosy. Of the 5376 eligible healthy contacts, 3536 were vaccinated, 30 of whom were excluded due to previous or current tuberculosis, or HIV. In 18 years of follow up, 122 (2.15%) incident cases were diagnosed (58 vaccinated and 64 not), 28 occurring in the first year of follow up (21 vaccinated, 16 with no scar). The protection conferred by BCG was 56% and was not substantially affected by previous BCG vaccination (50% with a scar and 59% without). The risk of tuberculoid leprosy during the initial months was high among those vaccinated with no scar. However, it had substantially declined by the first year and in the following years, when the protection rate in this group reached 80%. Since Brazil is endemic for leprosy and the detection rate is not declining satisfactorily, vaccinating all contacts could be an effective means of substantially reducing the incidence of leprosy.

Randomization and baseline transmission in vaccine field trials.

In randomized trials, the treatment assignment mechanism is independent of the outcome of interest and other covariates thought to be relevant in determining this outcome. It also allows, on average, for a balanced distribution of these covariates in the vaccine and placebo groups. Randomization, however, does not guarantee that the estimated effect is an unbiased estimate of the biological effect of interest. We show how exposure to infection can be a confounder even in randomized vaccine field trials. Based on a simple model of the biological efficacy of interest, we extend the arguments on comparability and collapsibility to examine the limits of randomization to control for unmeasured covariates. Estimates from randomized, placebo-controlled Phase III vaccine field trials that differ in baseline transmission are not comparable unless explicit control for baseline transmission is taken into account.

A new model for the population pharmacokinetics of didanosine in healthy subjects.

Didanosine (ddI) is a component of highly active antiretroviral therapy drug combinations, used especially in resource-limited settings and in zidovudine-resistant patients. The population pharmacokinetics of ddI was evaluated in 48 healthy volunteers enrolled in two bioequivalence studies. These data, along with a set of co-variates, were the subject of a nonlinear mixed-effect modeling analysis using the NONMEM program. A two-compartment model with first order absorption (ADVAN3 TRANS3) was fitted to the serum ddI concentration data. Final pharmacokinetic parameters, expressed as functions of the co-variates gender and creatinine clearance (CL CR), were: oral clearance (CL = 55.1 + 240 x CL CR + 16.6 L/h for males and CL = 55.1 + 240 x CL CR for females), central volume (V2 = 9.8 L), intercompartmental clearance (Q = 40.9 L/h), peripheral volume (V3 = 62.7 + 22.9 L for males and V3 = 62.7 L for females), absorption rate constant (Ka = 1.51/h), and dissolution time of the tablet (D = 0.43 h). The intraindividual (residual) variability expressed as coefficient of variation was 13.0%, whereas the interindividual variability of CL, Q, V3, Ka, and D was 20.1, 75.8, 20.6, 18.9, and 38.2%, respectively. The relatively high (>30%) interindividual variability for some of these parameters, observed under the controlled experimental settings of bioequivalence trials in healthy volunteers, may result from genetic variability of the processes involved in ddI absorption and disposition.

A new model for the population pharmacokinetics of didanosine in healthy subjects

Didanosine (ddI) is a component of highly active antiretroviral therapy drug combinations, used especially in resource-limited settings and in zidovudine-resistant patients. The population pharmacokinetics of ddI was evaluated in 48 healthy volunteers enrolled in two bioequivalence studies. These data, along with a set of co-variates, were the subject of a nonlinear mixed-effect modeling analysis using the NONMEM program. A two-compartment model with first order absorption (ADVAN3 TRANS3) was fitted to the serum ddI concentration data. Final pharmacokinetic parameters, expressed as functions of the co-variates gender and creatinine clearance (CL CR), were: oral clearance (CL = 55.1 + 240 x CL CR + 16.6 L/h for males and CL = 55.1 + 240 x CL CR for females), central volume (V2 = 9.8 L), intercompartmental clearance (Q = 40.9 L/h), peripheral volume (V3 = 62.7 + 22.9 L for males and V3 = 62.7 L for females), absorption rate constant (Ka = 1.51/h), and dissolution time of the tablet (D = 0.43 h). The intraindividual (residual) variability expressed as coefficient of variation was 13.0 percent, whereas the interindividual variability of CL, Q, V3, Ka, and D was 20.1, 75.8, 20.6, 18.9, and 38.2 percent, respectively. The relatively high (>30 percent) interindividual variability for some of these parameters, observed under the controlled experimental settings of bioequivalence trials in healthy volunteers, may result from genetic variability of the processes involved in ddI absorption and disposition.

The impact of imperfect vaccines on the evolution of HIV virulence.

A theoretical framework is proposed on which some hypotheses related to the impact of imperfect vaccines on the evolution of HIV virulence can be tested. For this, a linear increase of risk behaviour with vaccine efficacy is assumed. This is based on the hypothesis that people are prone to relax preventive measures by knowing that they and their partners are vaccinated and that this effect is more intense the more effective the vaccine is known to be. An additional, and perhaps more important hypothesis is related to the theoretical possibility that increased risk behaviour of some vaccinated individuals in partially protected populations could act as a selective pressure toward more virulent HIV strains. Those hypotheses were tested by a mathematical model that considers three different HIV strains competing against each other in a population partially protected by imperfect vaccines of distinct efficacies. Simulations of the model demonstrated that, under the above hypotheses, there is a shift in HIV virulence towards more aggressive strains with increase in vaccine efficacy, associated with a marked reduction in the total amount of transmission and, consequently, in the prevalence of HIV. Potential ways for further testing the theory/model and the implications of the results are discussed.

A modelling analysis of pertussis transmission and vaccination in Rio de Janeiro, Brazil.

Pertussis is an infectious respiratory disease for which mass vaccination is an effective preventive strategy. In many developed countries, where high vaccination coverage has been maintained for approximately 50 years, re-emergence of the disease has been observed in all age groups. In the municipality of Rio de Janeiro (RJ), where vaccination started in the 1980s, surveillance data show no sign of disease re-emergence. We developed a mathematical model that incorporates the major demographic aspects of a large urban centre in a developing nation, in addition to the most important epidemiological aspects of disease transmission. Parameter values were estimated based on RJ demographic and vaccine coverage data. Overall, all vaccination strategies determined a major decrease (over 95% decrease when compared to the pre-vaccine era) in the incidence of primary infections (occurring in individuals who have never been immunized through infection or vaccine). On the other hand, the strategies (a) three doses at age 2-11 months, (b) three doses plus booster at age 12-23 months, (c) three doses plus booster at age 4-5 years, and (d) three doses plus both boosters, differently affected the incidence of secondary infections (occurring in previously infected/vaccinated individuals). Given that the immunity against pertussis wanes with time and that the infectious agent has not been eliminated from the population, it is expected that pertussis will continue to be a problem in RJ. Actually, since immunity acquired from vaccine wanes faster than disease-acquired immunity and the possibility of natural boosters has decreased with mass vaccination, an increase in the incidence of secondary infections among older age groups is expected (and predicted by the model). Possible explanations as to why this dynamics is not captured by the RJ surveillance system are discussed. A poorly effective surveillance system and a lack of awareness regarding loss of immunity and the possibility of pertussis infection in older age groups are among them. Finally, we bring attention to the need of (i) field studies for the measurement of pertussis incidence in adolescents and adults; (ii) better understanding of the transmission dynamics currently occurring in RJ, and (iii) re-evaluation of vaccination strategies with the possible introduction of acellular vaccines for the vaccination of older individuals.

CYP2A6 genetic polymorphisms and correlation with smoking status in Brazilians.

We investigated polymorphisms of cytochrome P450 2A6 (CYP2A6) and its association with smoking habits in 412 healthy Brazilians, self-recognized as white (n=147), black (n=123) and intermediate (n=142), and classified as smokers (n=205, including 61 ex-smokers) and nonsmokers (n=207). The frequencies of the variant alleles CYP2A6(*)1B, CYP2A6(*)2, CYP2A6(*)4 and CYP2A6(*)9 in the overall study population were 29.9, 1.7, 0.5 and 5.7%, respectively. Significant differences in the CYP2A6 allelic distribution were observed across the three population subgroups. There was a statistically significant trend for decreasing frequency of CYP2A6(*)1B from white to intermediate and to black persons. An association between CYP2A6 genotype and smoking dependence was detected, which could not be explained by the expected phenotypic activity of CYP2A6. In white and intermediate persons, the odds ratio (OR) of being smokers vs nonsmokers was 0.07 (95% CI 0.02-0.20; P<0.001) and 0.27 (95% CI 0.12-0.61; P<0.001), respectively, for genotypes including allele CYP2A6(*)1B, as compared to wild-type homozygous. In contrast, the corresponding OR in black Brazilians was 1.34 (95% CI 0.57-3.17; P=0.46). These data suggest that the CYP2A6(*)1B is associated with smoking dependence in white and intermediate, but not black Brazilians.

Risk assessment of yellow fever urbanization in Rio de Janeiro, Brazil.

Yellow fever (YF), an arthropod-borne viral disease, occurs in regions of tropical America and Africa. Sylvatic YF is endemic in the north and west of Brazil. Urban YF, on the other hand, has not been reported in the country since 1942. However, the widespread presence of the YF urban vector in Brazil has lead to concern about the potential re-emergence of YF in urban centres. Here, we assess the risk of YF emergence in the city of Rio de Janeiro, Brazil, by estimating the probability of infected individuals arriving from YF-endemic areas, and the probability of infective individuals triggering an epidemic. We found that the risk of urban YF emergence may reach values as high as 29% during the epizootic periods but the precision of the estimate is low.

Risk of fatal adverse events associated with 17DD yellow fever vaccine.

Yellow fever (YF), an acute infectious disease, is endemic in the north and central-west of Brazil. This disease can be prevented by the use of a vaccine. In Brazil, four fatal adverse events have been associated with the YF vaccine used in the country (17DD vaccine). We briefly describe the last two fatalities, and estimate the risk of 17DD-associated fatal adverse events under different epidemiological scenarios. Controversies regarding the appropriate denominator that enters the estimation of risk serve as a motivation for each proposed scenario. The statistical procedures used show optimum behaviour when assessing the risk of rare events. Risk estimates vary from 0.043 (95 % CI 0.017-0.110) to 2.131 (95 % CI 0.109-12.071) fatalities per million doses administered. The robust estimates of the risk of fatal adverse events we present constitute an important element in future risk-benefit analysis and point to the need for good quality vaccine coverage and adverse-events surveillance data to assess the risk of vaccination. Although vaccination of YF endemic regions is necessary to maintain low disease prevalence, preventive administration of YF vaccine to the entire population should be cautiously analysed.

Carbamazepine: a bioequivalence study and limited sampling modeling.

OBJECTIVES: To assess the bioequivalence of 2 formulations of carbamazepine and to develop and validate limited sampling strategy (LSS) models for estimating the area under the plasma concentration-time curve (AUC0-infinity) and the peak plasma concentration (Cmax) of carbamazepine. METHODS: Twenty-four (12 men, 12 women) healthy volunteers received single oral doses (400 mg) of carbamazepine, as reference and test conventional-release formulations, in a standard 2-sequence, 2-period crossover design. Bioequivalence assessment was based on the individual ratios of log-transformed values of AUC0-infinity and Cmax LSS modeling was developed in a training set of 12 randomly assigned volunteers and was validated on the other 12 subjects (validation set). RESULTS: Carbamazepine AUC0-infinity and Cmax can be accurately predicted (R2 = 0.89 - 0.95, precision = 2.6 - 7.2%) by single-point (72 h) and 2-point LSS models (6, 32 h), respectively. Bioequivalence assessments based on LSS-derived AUC0-infinity and Cmax provided results similar to those obtained using all the concentration-in-plasma data points, and indicated that the 2 formulations are bioequivalent. CONCLUSION: One-and 2-point LSS models provided accurate estimates of carbamazepine's AUC0-infinity and Cmax, and allowed correct assessment of bioequivalence between the formulations studied.

Malnutrition and susceptibility to enteroparasites: reinfection rates after mass chemotherapy.

The evidence that relates malnutrition to enteroparasite infections arises from studies that demonstrate the improvement of nutritional indicators after antiparasitism treatment. However, the role of malnutrition as an aggravating factor to the susceptibility to enteroparasite infections is still not fully understood. We investigated the correlation between malnutrition and enteroparasite infection after mass chemotherapy, in a poor city of São Paulo State, Brazil. The sample comprised 759 children between 1 and 10 years of age of whom 585 were followed up for a period of 1 year and periodically assessed for reinfection with enteroparasites. One year of follow-up after mass chemotherapy demonstrated that 38 of the undernourished children were reinfected with enteroparasites, as compared with 25 of the eutrophic children (P = 0.033). The survival multivariate analysis demonstrated that, after controlling for the potential confounding variables, maternal literacy and per capita income rate, malnutrition was associated with susceptibility to reinfection (P = 0.13). We demonstrate that, although maternal literacy and per capita income rate are indeed confounding variables, malnutrition contributes to an increase in the risk of enteroparasite infections.

Limited-sampling strategy models for estimating the pharmacokinetic parameters of 4-methylaminoantipyrine, an active metabolite of dipyrone

Bioanalytical data from a bioequivalence study were used to develop limited-sampling strategy (LSS) models for estimating the area under the plasma concentration versus time curve (AUC) and the peak plasma concentration (Cmax) of 4-methylaminoantipyrine (MAA), an active metabolite of dipyrone. Twelve healthy adult male volunteers received single 600 mg oral doses of dipyrone in two formulations at a 7-day interval in a randomized, crossover protocol. Plasma concentrations of MAA (N = 336), measured by HPLC, were used to develop LSS models. Linear regression analysis and a "jack-knife" validation procedure revealed that the AUC0- and the Cmax of MAA can be accurately predicted (R²>0.95, bias <1.5 percent, precision between 3.1 and 8.3 percent) by LSS models based on two sampling times. Validation tests indicate that the most informative 2-point LSS models developed for one formulation provide good estimates (R²>0.85) of the AUC (0-infinity) or Cmax for the other formulation. LSS models based on three sampling points (1.5, 4 and 24 h), but using different coefficients for AUC(0-infinity) and Cmax, predicted the individual values of both parameters for the enrolled volunteers (R²>0.88, bias = -0.65 and -0.37 percent, precision = 4.3 and 7.4 percent) as well as for plasma concentration data sets generated by simulation (R²>0.88, bias = -1.9 and 8.5 percent, precision = 5.2 and 8.7 percent). Bioequivalence assessment of the dipyrone formulations based on the 90 percent confidence interval of log-transformed AUC(0-infinity) and Cmax provided similar results when either the best-estimated or the LSS-derived metrics were used