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We investigated the expression and distribution of 5 cytoadhesion receptors for the Plasmodium falciparum erythrocyte membrane protein 1 in 12 regions of post-mortem brains of 50 Malawian children, that is, 27 with the clinical and pathological diagnosis of cerebral malaria (CM) and 23 with a non-malarial cause of death. We quantified the expression of each receptor by microvascular endothelium and the colocalization of receptor-expressing microvessels with sequestered infected red blood cells (iRBC) and calculated a receptor-independent sequestration ratio. There were differences in the level of expression and regional distribution of the five receptors: ICAM-1 was the most widely expressed receptor, followed by CD36, VCAM-1, E-selectin, and thrombospondin. Receptor-expressing microvessels were most numerous in the frontal lobe and least numerous in the brainstem and cerebellum. Colocalization of receptor-expressing endothelial cells with iRBC was present in all brain regions; it was highest for ICAM-1 and CD36 and greatest in the frontal lobe. The sequestration ratios were close to 100% for all receptors across all brain regions and were similar in cerebral and extracerebral microvessels. Receptor expression and colocalization ratios were greater in the brain than in the lung, heart, liver, spleen, and subcutaneous tissue. These differences in cerebral endothelial expression of cytoadhesion receptors and their preferential regional distribution may underpin differences in iRBC sequestration and lesion development in CM. Moreover, greater expression of these receptors in the brain vs peripheral organs may explain a comparatively greater degree of iRBC sequestration in the brain.

Negative control outcomes (NCOs) are useful tools for hidden bias detection, but empirical evidence validating NCOs for COVID-19 is lacking. To address this gap, we examined the blinded phase of the randomized, placebo-controlled Coronavirus Vaccine Efficacy (COVE; NCT04470427) trial of the mRNA-1273 COVID-19 vaccine. We confirmed that acute respiratory illness with a positive test for a non-SARS-CoV-2 respiratory pathogen on a multiplex PCR panel was a valid NCO for COVID-19, considering that it was unaffected by vaccination (vaccine efficacy, VE = 3.3% (95% CI, −22.3 to 23.6)) yet strongly associated with COVID-19 (odds ratio = 2.95 (95% CI, 2.00, 4.24)). Subsequently, we leveraged non-SARS-CoV-2 infections to detect bias in time-varying VE estimates from COVE’s blinded and booster phases. Balanced incidence of non-SARS-CoV-2 infection between vaccinated and unvaccinated COVID-19-free risk sets suggested low selection bias in VE estimates of two-dose mRNA-1273 against COVID-19 during the blinded phase (VE = 92.5% (95% CI, 88.8, 94.9) 14 days post-dose-two, stable for 5 months). In COVE’s booster phase, higher non-SARS-CoV-2 incidence was observed after the single booster (intensity ratio, IR = 2.38 (95% CI, 1.75, 3.25) 14 days post-boost), suggesting that booster VE estimates may underestimate the true VE against COVID-19. Our findings demonstrate the potential of off-target infections for unraveling complex biases in COVID-19 vaccine studies.

HIV vaccine trial participants include sexually active cisgender females who agree to avoid pregnancy during the active vaccination period. Nevertheless, some pregnancies occur in almost all studies. We examined contraceptive use, pregnancy incidence, and the relationship between pregnancy and HIV seroconversion in one HIV vaccine trial. We performed an exploratory analysis of data collected for HVTN 705/HPX2008, a phase IIb HIV vaccine trial enrolling cisgender women across 23 sites in five southern African countries. Baseline characteristics and contraceptive use were assessed among participants who became pregnant and those who did not during the active vaccination phase (months 0–15). Pregnancy incidence rates were calculated for this phase and the duration of follow up (36 months). Cox regression analysis was used to assess factors associated with incident pregnancy. There were 2,636 participants who received at least one vaccine or placebo dose (mean age: 23 years, standard deviation: 3 years). At enrolment, when contraception was required, 62.9% reported using injectable contraceptives. Overall pregnancy rate was 2.95 per 100 person-years (95% CI: 2.40, 3.58), with 101 pregnancies reported by month 15. Cumulative incidence of pregnancy at month 15 was similar between trial arms (log-rank p = 0.688). Each additional year of age was associated with an 8% decrease in pregnancy incidence (p = 0.014). Women aged 31–35 years had the lowest pregnancy incidence [1.75 (0.48, 4.48) per 100 person-years]. In a Cox regression analysis covering months 0–15, all contraceptive methods significantly reduced the incidence of pregnancy compared to no contraceptive use. Oral contraception was associated with the least reduction in pregnancy risk; implants were associated with the most reduction in pregnancy risk (p < 0.001).In HVTN 705/HPX2008, higher incidence of pregnancy was associated with younger age and oral contraception (compared to other methods). These data may inform future designs of HIV prevention or vaccine trials.

Adjustment for prognostic baseline variables can reduce bias due to covariate imbalance and increase efficiency in randomized trials. While the use of covariate adjustment in late-phase trials is justified by favorable large-sample properties, it is seldom used in small, early-phase studies, due to uncertainty in which variables are prognostic and the potential for precision loss, type I error rate inflation, and undercoverage of confidence intervals. To address this problem, we consider adjustment for a valid negative control outcome (NCO), or an auxiliary post-randomization outcome believed to be completely unaffected by treatment but more highly correlated with the primary outcome than baseline covariates. We articulate the assumptions that permit adjustment for NCOs without producing post-randomization selection bias, and describe plausible data-generating models where NCO adjustment can improve upon adjustment for baseline covariates alone. In numerical experiments, we illustrate performance and provide practical recommendations regarding model selection and finite-sample variance corrections. We apply our methods to the reanalysis of two early-phase vaccine trials in HIV exposed uninfected (HEU) infants, where we demonstrate that adjustment for auxiliary post-baseline immunological parameters can enhance the precision of vaccine effect estimates relative to standard approaches that avoid adjustment or adjust for baseline covariates alone.

Autopsy studies of children dying of cerebral malaria (CM) have revealed that those with malarial retinopathy exhibited high levels of sequestration in the cerebral vasculature, whereas children with retinopathy-negative CM exhibited lower sequestration levels and possible nonmalarial causes of death. This suggests that children dying of retinopathy-negative CM have nonmalarial coma etiologies with concomitant incidental parasitemia, which is common in high malaria transmission areas. Subsequent studies have challenged this assertion, positing that retinopathy-negative CM and retinopathy-positive CM are variants of the same disease pathophysiology or host biology, both caused by acute malaria infection. We recently determined that electroencephalography (EEG) can be used to discriminate between a malarial coma (CM) and a nonmalarial coma. To better understand the contribution of acute malaria infection in the pathophysiology of retinopathy-negative CM, we compared qualitative and quantitative EEG findings from 30-minute EEG recordings of Malawian children aged 3 months to 14 years hospitalized at Queen Elizabeth Central Hospital with retinopathy-negative CM, retinopathy-positive CM, and nonmalarial coma. Neither qualitative nor quantitative EEG interpretation methods allow for the discrimination between children with retinopathy-positive CM and those with retinopathy-negative CM. Conversely, quantitative EEG readily differentiated children with retinopathy-negative CM from those with nonmalarial coma (area under the receiving operating characteristic [AUROC] curve of 0.83). When combining qualitative and quantitative EEG interpretation methods, the ability of EEG to distinguish retinopathy-negative CM from nonmalarial EEG increases (AUROC of 0.87). The EEGs of children with retinopathy-negative CM are similar to those of children with retinopathy-positive CM and significantly different from those of children with nonmalarial coma, supporting the hypothesis that acute malarial infection is pathophysiologically important in retinopathy-negative CM.

In an observational study, it is common to leverage known null effects to detect bias. One such strategy is to set aside a placebo sample – a subset of data immune from the hypothesized cause-and-effect relationship. Existence of an effect in the placebo sample raises concerns about unmeasured confounding bias while the absence of it helps corroborate the causal conclusion. This article describes a framework for using a placebo sample to detect and remove bias. We state the identification assumptions and develop estimation and inference methods based on outcome regression, inverse probability weighting, and doubly robust approaches. Simulation studies investigate the finite-sample performance of the proposed methods. We illustrate the methods using an empirical study of the effect of the earned income tax credit on infant health.

With limited access to mRNA COVID-19 vaccines in lower income countries, and people living with HIV (PLWH) largely excluded from clinical trials, Part A of the multicentre CoVPN 3008 (Ubuntu) study aimed to assess the safety of mRNA-1273, the relative effectiveness of hybrid versus vaccine immunity, and SARS-CoV-2 viral persistence among PLWH in East and Southern Africa during the omicron outbreak.Previously unvaccinated adults with HIV and/or other comorbidities associated with severe COVID-19 received either one (hybrid immunity) or two (vaccine immunity) 100-mcg doses of ancestral strain mRNA-1273 in the first month, depending on baseline evidence of prior SARS-CoV-2 infection. In a prospective cohort study design, we used covariate-adjusted Cox regression and counterfactual cumulative incidence methods to determine the hazard ratio and relative risk of COVID-19 and severe COVID-19 with hybrid versus vaccine immunity within six months. The ongoing Ubuntu study is registered on ClinicalTrials.gov (NCT05168813) and this work was conducted from December 2021 to March 2023.Between December 2021 and September 2022, 14,237 participants enrolled, and 14,002 (83% PLWH, 69% SARS-CoV-2 seropositive) were included in the analyses. Vaccinations were safe and well tolerated. Common adverse events were pain or tenderness at the injection site (26.7%), headache (20.4%), and malaise (20.3%). Severe adverse events were rare (0.8% of participants after the first and 1.1% after the second vaccination), and none were life-threatening or fatal. Among PLWH, the median CD4 count was 635 cells/μl and 18.5% had HIV viraemia. The six-month cumulative incidences in the hybrid immunity and vaccine immunity groups were 2.02% (95% confidence interval [CI] 1.61–2.44) and 3.40% (95% CI 2.30–4.49) for COVID-19, and 0.048% (95% CI 0.00–0.10) and 0.32% (95% CI 0.59–0.63) for severe COVID-19. Among all PLWH the hybrid immunity group had a 42% lower hazard rate of COVID-19 (hazard ratio [HR] 0.58; 95% CI 0.44–0.77; p < 0.001) and a 73% lower hazard rate of severe COVID-19 (HR 0.27; 95% CI 0.07–1.04; p = 0.056) than the vaccine immunity group, but this effect was not seen among PLWH with CD4 counts <350 cells/μl or HIV viraemia. Twenty PLWH had persistent SARS-CoV-2 virus at least 50 days.Hybrid immunity was associated with superior protection from COVID-19 compared to vaccine immunity with the ancestral mRNA-1273 vaccine. Persistent infections among immunocompromised PLWH may provide reservoirs for emerging variants.

Neutralizing antibody titer has been a surrogate endpoint for guiding COVID-19 vaccine approval and use, although the pandemic’s evolution and the introduction of variant-adapted vaccine boosters raise questions as to this surrogate’s contemporary performance. For 985 recipients of an mRNA second bivalent or monovalent booster containing various Spike inserts [Prototype (Ancestral), Beta, Delta, and/or Omicron BA.1 or BA.4/5] in the COVAIL trial (NCT05289037), titers against 5 strains were assessed as correlates of risk of symptomatic COVID-19 (“COVID-19”) and as correlates of relative (Pfizer-BioNTech Omicron vs. Prototype) booster protection against COVID-19 over 6 months of follow-up during the BA.2-BA.5 Omicron-dominant period. Consistently across the Moderna and Pfizer-BioNTech vaccine platforms and across all variant Spike inserts assessed, both peak and exposure-proximal (“predicted-at-exposure”) titers correlated with lower Omicron COVID-19 risk in individuals previously infected with SARS-CoV-2, albeit significantly less so in naïve individuals [e.g., exposure-proximal hazard ratio per 10-fold increase in BA.1 titer 0.74 (95% CI 0.59, 0.94) for naïve vs. 0.41 (95% CI 0.23, 0.64) for non-naïve; interaction p = 0.013]. Neutralizing antibody titer was a strong inverse correlate of Omicron COVID-19 in non-naïve individuals and a weaker correlate in naïve individuals, posing questions about how prior infection alters the neutralization correlate.

Many recent studies have probed status bias in the peer-review process of academic journals and conferences. In this article, we investigated the association between author metadata and area chairs’ final decisions (Accept/Reject) using our compiled database of 5,313 borderline submissions to the International Conference on Learning Representations from 2017 to 2022 under a matched observational study framework. We carefully defined elements in a cause-and-effect analysis, including the treatment and its timing, pre-treatment variables, potential outcomes (POs) and causal null hypothesis of interest, all in the context of study units being textual data and under Neyman and Rubin’s PO framework. We found some weak evidence that author metadata was associated with articles’ final decisions. We also found that, under an additional stability assumption, borderline articles from high-ranking institutions (top-30% or top-20%) were less favored by area chairs compared to their matched counterparts. The results were consistent in two different matched designs (odds ratio = 0.82 [95% confidence interval (CI): 0.67 to 1.00] in a first design and 0.83 [95% CI: 0.64 to 1.07] in a strengthened design) and most pronounced in the subgroup of articles with low ratings. We discussed how to interpret these results in the context of multiple interactions between a study unit and different agents (reviewers and area chairs) in the peer-review system.

For COVAIL recipients of a coronavirus disease 2019 (COVID-19) Sanofi booster vaccine, neutralizing antibody titers were assessed as a correlate of risk (CoR) of COVID-19. Peak and exposure-proximal titers were inverse CoRs with covariate-adjusted hazard ratios (95% confidence intervals) 0.30 (0.11, 0.78) and 0.25 (0.07, 0.85) per 10-fold increase in weighted average titer.