A pooled analysis of individual data from >5000 human immunodeficiency virus type 1 (HIV-1)–infected mothers and their infants from Africa and India who participated in 5 randomized trials shows that extended prophylaxis with nevirapine or with nevirapine and zidovudine significantly reduces postnatal HIV-1 infection.
Background. In resource-limited settings, mothers infected with human immunodeficiency virus type 1 (HIV-1) face a difficult choice: breastfeed their infants but risk transmitting HIV-1 or not breastfeed their infants and risk the infants dying of other infectious diseases or malnutrition. Recent results from observational studies and randomized clinical trials indicate daily administration of nevirapine to the infant can prevent breast-milk HIV-1 transmission.
Methods. Data from 5396 mother-infant pairs who participated in 5 randomized trials where the infant was HIV-1 negative at birth were pooled to estimate the efficacy of infant nevirapine prophylaxis to prevent breast-milk HIV-1 transmission. Four daily regimens were compared: nevirapine for 6 weeks, 14 weeks, or 28 weeks, or nevirapine plus zidovudine for 14 weeks.
Results. The estimated 28-week risk of HIV-1 transmission was 5.8% (95% confidence interval [CI], 4.3%–7.9%) for the 6-week nevirapine regimen, 3.7% (95% CI, 2.5%–5.4%) for the 14-week nevirapine regimen, 4.8% (95% CI, 3.5%–6.7%) for the 14-week nevirapine plus zidovudine regimen, and 1.8% (95% CI, 1.0%–3.1%) for the 28-week nevirapine regimen (log-rank test for trend, P < .001). Cox regression models with nevirapine as a time-varying covariate, stratified by trial site and adjusted for maternal CD4 cell count and infant birth weight, indicated that nevirapine reduces the rate of HIV-1 infection by 71% (95% CI, 58%–80%; P < .001) and reduces the rate of HIV infection or death by 58% (95% CI, 45%–69%; P < .001).
Conclusions. Extended prophylaxis with nevirapine or with nevirapine and zidovudine significantly reduces postnatal HIV-1 infection. Longer duration of prophylaxis results in a greater reduction in the risk of infection.
breast milk; HIV; nevirapine
Assessing per-protocol treatment effcacy on a time-to-event endpoint is a common
objective of randomized clinical trials. The typical analysis uses the same method employed for the
intention-to-treat analysis (e.g., standard survival analysis) applied to the subgroup meeting
protocol adherence criteria. However, due to potential post-randomization selection bias, this
analysis may mislead about treatment efficacy. Moreover, while there is extensive literature on
methods for assessing causal treatment effects in compliers, these methods do not apply to a common
class of trials where a) the primary objective compares survival curves, b) it is inconceivable to
assign participants to be adherent and event-free before adherence is measured, and c) the exclusion
restriction assumption fails to hold. HIV vaccine efficacy trials including the recent RV144 trial
exemplify this class, because many primary endpoints (e.g., HIV infections) occur before adherence
is measured, and nonadherent subjects who receive some of the planned immunizations may be partially
protected. Therefore, we develop methods for assessing per-protocol treatment efficacy for this
problem class, considering three causal estimands of interest. Because these estimands are not
identifiable from the observable data, we develop nonparametric bounds and semiparametric
sensitivity analysis methods that yield estimated ignorance and uncertainty intervals. The methods
are applied to RV144.
As-treated; Bounds; Causal inference; Exclusion restriction; Ignorance region; Intention to treat; Principal stratification; Selection bias; Survival analysis
Background. Limited data exist on cotrimoxazole prophylactic treatment (CPT)
in pregnant women, including protection against malaria versus standard intermittent preventive
therapy with sulfadoxine-pyrimethamine (IPTp). Methods. Using observational
data we examined the effect of CPT in HIV-infected pregnant women on malaria during pregnancy,
low birth weight and preterm birth using proportional hazards, logistic, and log binomial regression,
respectively. We used linear regression to assess effect of CPT on CD4 count.
Results. Data from 468 CPT-exposed and 768 CPT-unexposed women
were analyzed. CPT was associated with protection against malaria versus
IPTp (hazard ratio: 0.35, 95% Confidence Interval (CI): 0.20, 0.60). After
adjustment for time period this effect was not statistically significant (adjusted hazard
ratio: 0.66, 95% CI: 0.28, 1.52). Among women receiving and not receiving CPT,
rates of low birth weight (7.1% versus 7.6%) and preterm birth (23.5% versus 23.6%) were similar.
CPT was associated with lower CD4 counts 24 weeks postpartum in women
receiving (−77.6 cells/μL, 95% CI: −125.2, −30.1) and not
receiving antiretrovirals (−33.7 cells/μL, 95% CI: −58.6, −8.8).
Conclusions. Compared to IPTp, CPT provided comparable protection against malaria in HIV-infected
pregnant women and against preterm birth or low birth weight. Possible implications of CPT-associated lower CD4 postpartum warrant further examination.
In randomized trials to prevent breast milk transmission of human immunodeficiency virus (HIV) from mother to infant, investigators are often interested in assessing the effect of a treatment or intervention on the cumulative risk of HIV infection by time (age) t in infants who are alive and uninfected at a certain time point τ0 < t. Such comparisons are challenging for two reasons. First, infants are typically randomized at birth (time 0 < τ0) such that comparisons between trial arms among the subset of infants alive and uninfected at τ0 are subject to selection bias. Second, in most mother-to-child transmission (MTCT) trials competing risks are often present, such as death or cessation of breastfeeding prior to HIV infection. In this paper we present methods for assessing the causal effect of a treatment on competing risk outcomes within principal strata. In MTCT trials, the causal effect of interest is that of treatment on the risk of HIV infection by time t > τ0 within the principal stratum of infants who would be alive and uninfected by τ0 regardless of randomization assignment. Large sample non-parametric bounds and a semi-parametric sensitivity analysis model are developed for drawing inference about this causal effect. A simulation study is presented demonstrating that the proposed methods perform well in finite samples. The proposed methods are applied to a large, recent MTCT trial.
Causal inference; Infectious diseases; Principal stratification; Sensitivity analysis
Causal inference; infectious disease; infectiousness; interference; principal stratification; vaccine efficacy
The p16INK4a tumor suppressor gene is a mediator of cellular senescence and has been suggested to be a biomarker of ‘molecular’ age in several tissues including T-cells. To determine the association of both active and suppressed HIV infection with T-cell aging, T-cell p16INK4a expression was compared between 60 HIV+ suppressed subjects, 23 HIV+ untreated subjects, and 18 contemporaneously collected HIV-negative controls, as well as 148 HIV-negative historical samples. Expression did not correlate with chronologic age in untreated HIV+ patients, consistent with an effect of active HIV replication on p16INK4a expression. In patients on cART with suppressed viral loads, however, p16INK4a levels were similar to uninfected controls and correlated with chronologic age, with a trend toward an inverse correlation with CD4 count. These data show that p16INK4a is a reliable biomarker of T cell aging in HIV+ patients with suppressed viral loads and suggest that poor CD4 cell recovery on cART may be associated with increased T-cell expression of p16INK4a, a marker of cellular senescence.
If a vaccine does not protect individuals completely against infection, it could still reduce infectiousness of infected vaccinated individuals to others. Typically, vaccine efficacy for infectiousness is estimated based on contrasts between the transmission risk to susceptible individuals from infected vaccinated individuals compared with that from infected unvaccinated individuals. Such estimates are problematic, however, because they are subject to selection bias and do not have a causal interpretation. Here, we develop causal estimands for vaccine efficacy for infectiousness for four different scenarios of populations of transmission units of size two. These causal estimands incorporate both principal stratification, based on the joint potential infection outcomes under vaccine and control, and interference between individuals within transmission units. In the most general scenario, both individuals can be exposed to infection outside the transmission unit and both can be assigned either vaccine or control. The three other scenarios are special cases of the general scenario where only one individual is exposed outside the transmission unit or can be assigned vaccine. The causal estimands for vaccine efficacy for infectiousness are well defined only within certain principal strata and, in general, are identifiable only with strong unverifiable assumptions. Nonetheless, the observed data do provide some information, and we derive large sample bounds on the causal vaccine efficacy for infectiousness estimands. An example of the type of data observed in a study to estimate vaccine efficacy for infectiousness is analyzed in the causal inference framework we developed.
causal inference; principal stratification; interference; infectious disease; vaccine
Background.Little is known about type-specific associations between prevalent human papillomavirus (HPV) infections and risk of acquiring other HPV types in men. Data on natural clustering of HPV types are needed as a prevaccine distribution to which postvaccine data can be compared.
Methods.Using data from a randomized controlled trial of male circumcision in Kisumu, Kenya, adjusted mean survival ratios were estimated for acquisition of any-HPV, high-risk (HR) HPV, and individual HR-HPV types among men uninfected as compared to those infected with vaccine-relevant HPV types 16, 18, 31, 45, 6, or 11 at baseline.
Results.Among 1097 human immunodeficiency virus–negative, uncircumcised men, 2303 incident HPV infections were detected over 2534 person-years of follow-up. Although acquisition of individual HR-HPV types varied by baseline HPV type, there was no clear evidence of shorter times to acquisition among men without vaccine-relevant HPV-16, -18, -31, -45, -6, or -11 infections at baseline, as compared to men who did have these infections at baseline.
Conclusions.These prospective data on combinations of HPV infections over time do not suggest the potential for postvaccination HPV type replacement. Future surveillance studies are needed to definitely determine whether elimination of HPV types by vaccination will alter the HPV type distribution in the population.
Racial differences in antiretroviral treatment responses remain incompletely explained and may be a consequence of differential pharmacokinetics (PK) associated with race. Raltegravir, an inhibitor of HIV-1 integrase, is commonly used in the treatment of HIV-infected patients, many of whom are African-American. However, there are few data regarding the PK of raltegravir in African-Americans. HIV-infected men and women, self-described as African-American and naive to antiretroviral therapy were treated with raltegravir (RAL) at 400 mg twice a day, plus a fixed dose of tenofovir-emtricitabine (TDF/FTC) at 300 mg/200 mg once daily. Intensive PK sampling was conducted over 24 h at week 4. Drug concentrations at two trough values of 12 and 24 h after dosing (C12 and C24), area under the concentration-curve values (AUC), maximum drug concentration (Cmax), and the time at which this concentration occurred (Tmax) in plasma were estimated with noncompartmental pharmacokinetic methods and compared to data from a subset of white subjects randomized to the RAL twice a day (plus TDF/FTC) arm of the QDMRK study, a phase III study of the safety and efficacy of once daily versus twice daily RAL in treatment naive patients. A total of 38 African-American participants were enrolled (90% male) into the REAL cohort with the following median baseline characteristics: age of 36 years, body mass index (BMI) of 23 kg/m2, and a CD4 cell count of 339/ml. Plasma HIV RNA levels were below 200 copies/ml in 95% of participants at week 4. The characteristics of the 16 white QDMRK study participants were similar, although fewer (69%) were male, the median age was higher (45 years), and BMI was lower (19 kg/m2). There was considerable interindividual variability in RAL concentrations in both cohorts. Median C12 in REAL was 91 ng/ml (range, 10 to 1,386) and in QDMRK participants was 128 ng/ml (range, 15 to 1,074). The Cmax median concentration was 1,042 ng/ml (range, 196 to 10,092) for REAL and 1,360 ng/ml (range, 218 to 9,701) for QDMRK. There were no significant differences in any RAL PK parameter between these cohorts of African-American and white individuals. Based on plasma PK, and with similar adherence rates, the performance of RAL among HIV-infected African-Americans should be no different than that of infected patients who are white.
The RV144 vaccine trial in Thailand demonstrated that an HIV vaccine could prevent infection in humans and highlights the importance of understanding protective immunity against HIV. We used a nonhuman primate model to define immune and genetic mechanisms of protection against mucosal infection by the simian immunodeficiency virus (SIV). A plasmid DNA prime/recombinant adenovirus serotype 5 (rAd5) boost vaccine regimen was evaluated for its ability to protect monkeys from infection by SIVmac251 or SIVsmE660 isolates after repeat intrarectal challenges. Although this prime-boost vaccine regimen failed to protect against SIVmac251 infection, 50% of vaccinated monkeys were protected from infection with SIVsmE660. Among SIVsmE660-infected animals, there was an about one-log reduction in peak plasma virus RNA in monkeys expressing the major histocompatibility complex class I allele Mamu-A*01, implicating cytotoxic T lymphocytes in the control of SIV replication once infection is established. Among Mamu-A*01–negative monkeys challenged with SIVsmE660, no CD8+ T cell response or innate immune response was associated with protection against virus acquisition. However, low levels of neutralizing antibodies and an envelope-specific CD4+ T cell response were associated with vaccine protection in these monkeys. Moreover, monkeys that expressed two TRIM5 alleles that restrict SIV replication were more likely to be protected from infection than monkeys that expressed at least one permissive TRIM5 allele. This study begins to elucidate the mechanism of vaccine protection against immunodeficiency viruses and highlights the need to analyze these immune and genetic correlates of protection in future trials of HIV vaccine strategies.
Data on the acquisition of human papillomavirus (HPV) infection in men are limited, especially from developing regions including Africa. The objective of this study was to characterise and determine the risk factors of HPV acquisition among a cohort of uncircumcised men participating in a randomised controlled trial (RCT) of male circumcision in Kisumu, Kenya.
Penile exfoliated cell specimens were collected at baseline, 6- and 12-month follow-up visits from the glans/coronal sulcus and shaft of men enrolled in the control arm of the RCT between 2002 and 2005. All participants were HIV seronegative, aged 17–24 years at baseline and remained uncircumcised over follow-up. Specimens were tested with GP5+/6+ PCR to detect 44 HPV types. Parametric frailty models were used to assess risk factors of HPV incidence.
The median age of 966 participants was 20 years. The median follow-up time was 12.1 months. The incidence rate (IR) of any HPV infection was 49.3/1000 person-months with HPV16 having the highest IR (10.9/1000 person-months). The strongest risk factors for overall HPV incidence were bathing less frequently than daily (adjusted HR=2.6; 95% CI 1.0 to 6.5) and having ≥2 female sexual partners in the past year (adjusted HR=1.6; 95% CI 1.2 to 2.1).
HPV IRs were notably high in this cohort of high-risk, uncircumcised men from Kisumu, Kenya, with the number of sexual partners and bathing frequency being the strongest risk factors.
This article examines group testing procedures where units within a group (or pool) may be correlated. The expected number of tests per unit (i.e., efficiency) of hierarchical- and matrix-based procedures is derived based on a class of models of exchangeable binary random variables. The effect on efficiency of the arrangement of correlated units within pools is then examined. In general, when correlated units are arranged in the same pool, the expected number of tests per unit decreases, sometimes substantially, relative to arrangements that ignore information about correlation.
Composite sampling; Epitope mapping; Exchangeable binary random variables; Group testing; HIV; Matrix testing; Pooled testing
In resource-limited settings where no safe alternative to breastfeeding exists, WHO recommends that antiretroviral prophylaxis be given to either HIV-infected mothers or infants throughout breastfeeding. We assessed the effect of 28 weeks of maternal or infant antiretroviral prophylaxis on postnatal HIV infection at 48 weeks.
The Breastfeeding, Antiretrovirals, and Nutrition (BAN) Study was undertaken in Lilongwe, Malawi, between April 21, 2004, and Jan 28, 2010. 2369 HIV-infected breastfeeding mothers with a CD4 count of 250 cells per μL or more and their newborn babies were randomly assigned with a variable-block design to one of three, 28-week regimens: maternal triple antiretroviral (n=849); daily infant nevirapine (n=852); or control (n=668). Patients and local clinical staff were not masked to treatment allocation, but other study investigators were. All mothers and infants received one dose of nevirapine (mother 200 mg; infant 2 mg/kg) and 7 days of zidovudine (mother 300 mg; infants 2 mg/kg) and lamivudine (mothers 150 mg; infants 4 mg/kg) twice a day. Mothers were advised to wean between 24 weeks and 28 weeks after birth. The primary endpoint was HIV infection by 48 weeks in infants who were not infected at 2 weeks and in all infants randomly assigned with censoring at loss to follow-up. This trial is registered with ClinicalTrials.gov, number NCT00164736.
676 mother–infant pairs completed follow-up to 48 weeks or reached an endpoint in the maternal-antiretroviral group, 680 in the infant-nevirapine group, and 542 in the control group. By 32 weeks post partum, 96% of women in the intervention groups and 88% of those in the control group reported no breastfeeding since their 28-week visit. 30 infants in the maternal-antiretroviral group, 25 in the infant-nevirapine group, and 38 in the control group became HIV infected between 2 weeks and 48 weeks of life; 28 (30%) infections occurred after 28 weeks (nine in maternal-antiretroviral, 13 in infant-nevirapine, and six in control groups). The cumulative risk of HIV-1 transmission by 48 weeks was significantly higher in the control group (7%, 95% CI 5–9) than in the maternal-antiretroviral (4%, 3–6; p=0·0273) or the infant-nevirapine (4%, 2–5; p=0·0027) groups. The rate of serious adverse events in infants was significantly higher during 29–48 weeks than during the intervention phase (1·1 [95% CI 1·0–1·2] vs 0·7 [0·7–0·8] per 100 person-weeks; p<0·0001), with increased risk of diarrhoea, malaria, growth faltering, tuberculosis, and death. Nine women died between 2 weeks and 48 weeks post partum (one in maternal-antiretroviral group, two in infant-nevirapine group, six in control group).
In resource-limited settings where no suitable alternative to breastfeeding is available, antiretroviral prophylaxis given to mothers or infants might decrease HIV transmission. Weaning at 6 months might increase infant morbidity
US Centers for Disease Control and Prevention.
Human papillomavirus (HPV)-associated penile lesions in men may increase the risk of HPV transmission to their female partners. Risk factor data on HPV-associated penile lesions are needed from regions with a high burden of cervical cancer. Visual inspection of the penis was conducted using a colposcope at the 24-month visit among participants in a randomized controlled trial of male circumcision in Kenya, from May 2006 to October 2007. All photos were read independently by two observers for quality control. Penile exfoliated cells sampled from the glans/coronal sulcus and the shaft were tested for HPV DNA using GP5+/6+ PCR and for HPV16, 18 and 31 viral loads using a real time PCR assay. Of 275 men, 151 were circumcised and 124 uncircumcised. The median age was 22 years. Circumcised men had a lower prevalence of flat penile lesions (0.7%) versus uncircumcised (26.0%); adjusted odds ratio [OR]=0.02; 95% confidence interval [CI]: 0.003–0.1). Compared to men who were HPV-negative, men who were HPV DNA positive (OR=6.5; 95%CI: 2.4–17.5) or who had high HPV16/18/31 viral load (OR=5.2; 95%CI: 1.1–24.4) had higher odds of flat penile lesions. Among men with flat penile lesions, HPV56 (29.0%) and 16 (25.8%) were the most common types. Flat penile lesions are much more frequent in uncircumcised men, and associated with higher prevalence of HPV and higher viral loads. This study suggests that circumcision reduces the prevalence of HPV-associated flat lesions and may ultimately reduce male to female HPV transmission.
Human papillomavirus; Penile lesions; Men; Circumcision; Kenya
To estimate the association of antiretroviral therapy initiation with incident acquired immunodeficiency syndrome (AIDS) or death while accounting for time-varying confounding in a cost-efficient manner, the authors combined a case-cohort study design with inverse probability-weighted estimation of a marginal structural Cox proportional hazards model. A total of 950 adults who were positive for human immunodeficiency virus type 1 were followed in 2 US cohort studies between 1995 and 2007. In the full cohort, 211 AIDS cases or deaths occurred during 4,456 person-years. In an illustrative 20% random subcohort of 190 participants, 41 AIDS cases or deaths occurred during 861 person-years. Accounting for measured confounders and determinants of dropout by inverse probability weighting, the full cohort hazard ratio was 0.41 (95% confidence interval: 0.26, 0.65) and the case-cohort hazard ratio was 0.47 (95% confidence interval: 0.26, 0.83). Standard multivariable-adjusted hazard ratios were closer to the null, regardless of study design. The precision lost with the case-cohort design was modest given the cost savings. Results from Monte Carlo simulations demonstrated that the proposed approach yields approximately unbiased estimates of the hazard ratio with appropriate confidence interval coverage. Marginal structural model analysis of case-cohort study designs provides a cost-efficient design coupled with an accurate analytic method for research settings in which there is time-varying confounding.
acquired immunodeficiency syndrome; case-cohort studies; cohort studies; confounding bias; HIV; pharmacoepidemiology; selection bias
Vaccine regimens using different agents for priming and boosting have become popular for enhancing T cell and Ab responses elicited by candidate HIV/AIDS vaccines. Here we use a simian model to evaluate immunogenicity and protective efficacy of a recombinant modified vaccinia Ankara (MVA) vaccine in the presence and absence of a recombinant DNA prime. The simian vaccines and regimens represent prototypes for candidate HIV vaccines currently undergoing clinical testing.
Recombinant DNA and MVA immunogens expressed simian immunodeficiency virus (SIV)mac239 Gag, PR, RT, and Env sequences. Vaccine schedules tested inoculations of MVA at months 0, 2, and 6 (MMM regimen) or priming with DNA at months 0 and 2 and boosting with MVA at months 4 and 6 (DDMM regimen). Twelve weekly rectal challenges with the heterologous SIV smE660 were initiated at 6 months following the last immunization.
Both regimens elicited similar 61–64% reductions in the per challenge risk of SIVsmE660 transmission despite raising different patterns of immune responses. The DDMM regimen elicited higher magnitudes of CD4 T cells whereas the MMM regimen elicited higher titers and greater avidity Env-specific IgG and more frequent and higher titer SIV-specific IgA in rectal secretions. Both regimens elicited similar magnitudes of CD8 T cells. Magnitudes of T cell responses, specific activities of rectal IgA Ab, and the tested specificities for neutralization and antibody-dependent cellular cytotoxicity did not correlate with risk of infection. However, the avidity of Env-specific IgG had a strong correlation with the per challenge risk of acquisition, but only for the DDMM group.
We conclude that for the tested immunogens in rhesus macaques, the simpler MMM regimen is as protective as the more complex DDMM regimen.
Vaccine; Immunodeficiency virus; Simian immunodeficiency virus; DNA vaccine MVA vaccine; avidity in protection
Obesity is an independent risk factor for morbidity and mortality from pandemic influenza H1N1. Influenza is a significant public health threat, killing an estimated 250,000 to 500,000 worldwide each year. More than one in ten of the world’s adult population is obese and more than two-thirds of the US adult population is overweight or obese. No studies have compared humoral or cellular immune responses to influenza vaccination in healthy weight, overweight and obese populations despite clear public health importance.
The study employed a convenience sample to determine the antibody response to the 2009–2010 inactivated trivalent influenza vaccine (TIV) in healthy weight, overweight and obese participants at one and 11 months post vaccination. In addition, activation of CD8+ T cells and expression of interferon-γ and granzyme B were measured in influenza-stimulated peripheral blood mononuclear cell cultures.
BMI correlated positively with higher initial fold increase in IgG antibodies detected by ELISA to TIV, confirmed by HAI antibody in a subset study. However, eleven months post vaccination, higher BMI was associated with a greater decline in influenza antibody titers. PBMC’s challenged ex vivo with vaccine strain virus demonstrated that obese individuals had decreased CD8+ T cell activation and decreased expression of functional proteins compared with healthy weight individuals.
These results suggest obesity may impair the ability to mount a protective immune response to influenza virus.
obesity; influenza; vaccination; IgG antibodies; CD8+ T cells
We consider the optimal configuration of a square array group testing algorithm (denoted A2) to minimize the expected number of tests per specimen. For prevalence greater than 0.2498, individual testing is shown to be more efficient than A2. For prevalence less than 0.2498, closed form lower and upper bounds on the optimal group sizes for A2 are given. Arrays of dimension 2 × 2, 3 × 3, and 4 × 4 are shown to never be optimal. The results are illustrated by considering the design of a specimen pooling algorithm for detection of recent HIV infections in Malawi.
Background. There is little information on multiple human papillomavirus (HPV) infections and the potential for type competition in men, yet competition may impact the type-specific efficacy of HPV vaccination.
Methods. Among 2702 uncircumcised men in Kisumu, Kenya, who were seronegative for human immunodeficiency virus, the observed numbers of HPV types detected were compared with the expected number, which was simulated under the assumption of independent infections. To assess the potential for HPV type competition, adjusted odds ratios for pairwise combinations of prevalent HPV type infections were estimated using semi-Bayesian methods.
Results. Half of all men were HPV positive, of whom 57% had multiple HPV types. We observed men without HPV infection and with ≥4 HPV types more often than expected if infections were independent. No negative associations between individual HPV types were observed. HPV types 31, 39, 56, 58, and 59 were positively associated with both carcinogenic vaccine types HPV-16 and HPV-18 (2-sided P value <.05).
Conclusions. Men who were HPV infected were likely to test positive for >1 HPV type. Cross-sectional associations between individual HPV types were positive and did not appear to be type-specific. Thus, we did not identify HPV types that are candidates for potential HPV type competition in men.
The Data and Safety Monitoring Board (DSMB) for the Breastfeeding, Antiretrovirals, and Nutrition study, a clinical trial aimed to prevent postnatal HIV transmission, recommended halting randomization to the enhanced standard-of-care (control) arm. The 67 mother-infant pairs on the control arm and less than 21 weeks postpartum at the time of the DSMB recommendation were read a script informing them of the DSMB decision and offering them the the maternal or infant antiretroviral interventions for the remainder of the 28-week breastfeeding period. This paper describes the BAN study response to the DSMB decision and what the women on the control arm chose, when given a choice to start the maternal or infant antiretroviral interventions.
Postnatal HIV transmission; breastfeeding; antiretorival prophylaxis
Nicaragua was the first developing nation to implement universal infant rotavirus immunization with the pentavalent rotavirus vaccine (RV5). Initial studies of vaccine effectiveness in Nicaragua and other developing nations have focused on the prevention of hospitalizations and severe rotavirus diarrhea. However, rotavirus diarrhea is more commonly treated in the primary care setting, with only 1–3% of rotavirus cases receiving hospital care. We measured the prevalence of rotavirus infection in primary care clinics in León, Nicaragua, after introduction of the immunization program. In the post-vaccine period, 3.5% (95% confidence interval = 1.9–5.8) of children seeking care for diarrhea tested positive for rotavirus. A high diversity of rotavirus genotypes was encountered among the few positive samples. In conclusion, rotavirus was an uncommon cause of childhood diarrhea in this primary care setting after implementation of a rotavirus immunization program.
This commentary takes up Pearl's welcome challenge to clearly articulate the scientific value of principal stratification estimands that we and colleagues have investigated, in the area of randomized placebo-controlled preventive vaccine efficacy trials, especially trials of HIV vaccines. After briefly arguing that certain principal stratification estimands for studying vaccine effects on post-infection outcomes are of genuine scientific interest, the bulk of our commentary argues that the “causal effect predictiveness” (CEP) principal stratification estimand for evaluating immune biomarkers as surrogate endpoints is not of ultimate scientific interest, because it evaluates surrogacy restricted to the setting of a particular vaccine efficacy trial, but is nevertheless useful for guiding the selection of primary immune biomarker endpoints in Phase I/II vaccine trials and for facilitating assessment of transportability/bridging surrogacy.
principal stratification; causal inference; vaccine trial
We evaluated the efficacy of a maternal triple-drug antiretroviral regimen or infant nevirapine prophylaxis for 28 weeks during breast-feeding to reduce postnatal transmission of human immunodeficiency virus type 1 (HIV-1) in Malawi.
We randomly assigned 2369 HIV-1–positive, breast-feeding mothers with a CD4+ lymphocyte count of at least 250 cells per cubic millimeter and their infants to receive a maternal antiretroviral regimen, infant nevirapine, or no extended postnatal antiretroviral regimen (control group). All mothers and infants received perinatal prophylaxis with single-dose nevirapine and 1 week of zidovudine plus lamivudine. We used the Kaplan–Meier method to estimate the cumulative risk of HIV-1 transmission or death by 28 weeks among infants who were HIV-1–negative 2 weeks after birth. Rates were compared with the use of the log-rank test.
Among mother–infant pairs, 5.0% of infants were HIV-1–positive at 2 weeks of life. The estimated risk of HIV-1 transmission between 2 and 28 weeks was higher in the control group (5.7%) than in either the maternal-regimen group (2.9%, P = 0.009) or the infant-regimen group (1.7%, P<0.001). The estimated risk of infant HIV-1 infection or death between 2 and 28 weeks was 7.0% in the control group, 4.1% in the maternal-regimen group (P = 0.02), and 2.6% in the infant-regimen group (P<0.001). The proportion of women with neutropenia was higher among those receiving the antiretroviral regimen (6.2%) than among those in either the nevirapine group (2.6%) or the control group (2.3%). Among infants receiving nevirapine, 1.9% had a hypersensitivity reaction.
The use of either a maternal antiretroviral regimen or infant nevirapine for 28 weeks was effective in reducing HIV-1 transmission during breast-feeding. (ClinicalTrials.gov number, NCT00164736.)
A fundamental assumption usually made in causal inference is that of no interference between individuals (or units); that is, the potential outcomes of one individual are assumed to be unaffected by the treatment assignment of other individuals. However, in many settings, this assumption obviously does not hold. For example, in the dependent happenings of infectious diseases, whether one person becomes infected depends on who else in the population is vaccinated. In this article, we consider a population of groups of individuals where interference is possible between individuals within the same group. We propose estimands for direct, indirect, total, and overall causal effects of treatment strategies in this setting. Relations among the estimands are established; for example, the total causal effect is shown to equal the sum of direct and indirect causal effects. Using an experimental design with a two-stage randomization procedure (first at the group level, then at the individual level within groups), unbiased estimators of the proposed estimands are presented. Variances of the estimators are also developed. The methodology is illustrated in two different settings where interference is likely: assessing causal effects of housing vouchers and of vaccines.
Group-randomized trials; Potential outcomes; Stable unit treatment value assumption; SUTVA; Vaccine