Dynamic RMST curves for survival analysis in clinical trials.

BACKGROUND: The data from immuno-oncology (IO) therapy trials often show delayed effects, cure rate, crossing hazards, or some mixture of these phenomena. Thus, the proportional hazards (PH) assumption is often violated such that the commonly used log-rank test can be very underpowered. In these trials, the conventional hazard ratio for describing the treatment effect may not be a good estimand due to the lack of an easily understandable interpretation. To overcome this challenge, restricted mean survival time (RMST) has been strongly recommended for survival analysis in clinical literature due to its independence of the PH assumption as well as a more clinically meaningful interpretation. The RMST also aligns well with the estimand associated with the analysis from the recommendation in ICH E-9 (R1), and the test/estimation coherency. Currently, the Kaplan Meier (KM) curve is commonly applied to RMST related analyses. Due to some drawbacks of the KM approach such as the limitation in extrapolating to time points beyond the follow-up time, and the large variance at time points with small numbers of events, the RMST may be hindered. METHODS: The dynamic RMST curve using a mixture model is proposed in this paper to fully enhance the RMST method for survival analysis in clinical trials. It is constructed that the RMST difference or ratio is computed over a range of values to the restriction time τ which traces out an evolving treatment effect profile over time. RESULTS: This new dynamic RMST curve overcomes the drawbacks from the KM approach. The good performance of this proposal is illustrated through three real examples. CONCLUSIONS: The RMST provides a clinically meaningful and easily interpretable measure for survival clinical trials. The proposed dynamic RMST approach provides a useful tool for assessing treatment effect over different time frames for survival clinical trials. This dynamic RMST curve also allows ones for checking whether the follow-up time for a study is long enough to demonstrate a treatment difference. The prediction feature of the dynamic RMST analysis may be used for determining an appropriate time point for an interim analysis, and the data monitoring committee (DMC) can use this evaluation tool for study recommendation.

Integrated Safety Profile of a New Approved, Fully Liquid DTaP5-HB-IPV-Hib Vaccine.

BACKGROUND: DTaP5-HB-IPV-Hib is a fully liquid, hexavalent vaccine containing a 5-antigen pertussis component, approved since 2016 in Europe [Vaxelis; DTaP5-HB-IPV-Hib vaccine: Diphtheria, tetanus, pertussis (5 acellular components: pertussis toxoid [PT], filamentous haemagglutinin [FHA], pertactin (PRN), and fimbriae Types 2 and 3 [FIM]), hepatitis B (recombinant DNA: rDNA), poliomyelitis (inactivated) and Haemophilus influenzae type b conjugate vaccine (adsorbed); MCM Vaccine B.V., The Netherlands] for primary and booster vaccination in infants and toddlers against diphtheria, tetanus, pertussis, hepatitis B, poliomyelitis and invasive diseases caused by Haemophilus influenzae type b. The comparator vaccine (control) was INFANRIX hexa (GlaxoSmithKline Biologics S.A., Rixensart, Belgium) (DTaP3-IPV-HepB/Hib) in European studies and PENTACEL (DTaP5-IPV/Hib) (Sanofi Pasteur, Swiftwater, PA) in US studies. METHODS: Data from 6 studies were integrated and analyzed to provide a comprehensive safety profile. Numbers and proportions of subjects with adverse events (AEs) were summarized by treatment group. Group differences in proportion of AEs were calculated. RESULTS: Among the DTaP5-HB-IPV-Hib (N = 5223) and 2295 control (N = 2295) groups, solicited injection-site and systemic AEs were very common. Serious AEs were reported by 3.9% of DTaP5-HB-IPV-Hib and 3.7% of control subjects. Vaccine-related serious AEs occurred infrequently, 0.2% for both groups. Most AEs were mild-to-moderate and did not lead to subject withdrawal. Group differences for solicited systemic AEs were small (<3%) and not statistically significant, except for pyrexia (estimated difference 9.4% [95% CI: 6.7%-12%]). The difference was driven by the 2 US studies where the PENTACEL control group had a lower fever rate. Among European studies, there was no significant difference in rates of pyrexia between DTaP5-HB-IPV-Hib and INFANRIX hexa. CONCLUSIONS: The safety of DTaP5-HB-IPV-Hib is consistent with the safety profile of its components and similar to comparator vaccines, including INFANRIX hexa. The vaccine provides a new, fully liquid and convenient hexavalent vaccination option for use with various vaccination schedules in Europe.

A dynamic power prior for borrowing historical data in noninferiority trials with binary endpoint.

Traditionally, noninferiority hypotheses have been tested using a frequentist method with a fixed margin. Given that information for the control group is often available from previous studies, it is interesting to consider a Bayesian approach in which information is "borrowed" for the control group to improve efficiency. However, construction of an appropriate informative prior can be challenging. In this paper, we consider a hybrid Bayesian approach for testing noninferiority hypotheses in studies with a binary endpoint. To account for heterogeneity between the historical information and the current trial for the control group, a dynamic P value-based power prior parameter is proposed to adjust the amount of information borrowed from the historical data. This approach extends the simple test-then-pool method to allow a continuous discounting power parameter. An adjusted α level is also proposed to better control the type I error. Simulations are conducted to investigate the performance of the proposed method and to make comparisons with other methods including test-then-pool and hierarchical modeling. The methods are illustrated with data from vaccine clinical trials.

Postdose 3 G1 serum neutralizing antibody as correlate of protection for pentavalent rotavirus vaccine.

Although clinical trials of the pentavalent rotavirus vaccine (RotaTeq®, RV5) have demonstrated efficacy against RV gastroenteritis (RGE) in low and high-income settings, a clear correlate of protection or a measure of immune response that could predict efficacy has yet to be identified. This is the first time that immunogenicity data with both serum neutralized antibody (SNA) titers and anti-RV IgA titers from several clinical efficacy trials were pooled to provide a unique context for evaluating the correlation between immunogenicity and RGE risk or efficacy of RV5. The correlation between immunogenicity and RGE risk is evaluated with data at the individual subject level. The analyses show that higher Postdose 3 (PD3) G1 SNA titers are associated with lower odds of contracting any RGE. The correlation between immunogenicity and efficacy is assessed using aggregated population level data, which shows higher efficacy associated with higher PD3 G1 SNA geometric mean titer (GMT) ratio (between RV5 and placebo) and PD3 serum anti-RV IgA GMT ratio. Among high-income countries, efficacy plateaus over the range of PD3 G1 SNA GMT ratios and PD3 serum anti-RV IgA GMT ratios. From both individual- and population-level analyses, PD3 G1 SNA titers correlated most closely with the RGE risk or efficacy for RV5.

A Phase III Randomized, Double-blind, Clinical Trial of an Investigational Hexavalent Vaccine Given at Two, Three, Four and Twelve Months.

BACKGROUND: Combination vaccines simplify vaccination visits and improve coverage and timeliness. Diphtheria-tetanus toxoids-acellular pertussis 5, hepatitis B, inactivated poliovirus vaccine and Haemophilus influenzae type b (DTaP5-HB-IPV-Hib) is a new investigational, fully liquid, combination vaccine containing a 5-antigen pertussis component and is designed to protect against 6 infectious diseases. METHODS: In this multicenter, double-blind, comparator-controlled, phase III study (NCT01341639) conducted in Finland, Germany and Belgium, healthy infants were randomized 1:1 to receive 1 of 2 immunization regimens. The DTaP5-HB-IPV-Hib group received the investigational hexavalent vaccine (DTaP-HB-IPV-Hib) and the Control group received Infanrix-hexa (DTPa3-HBV-IPV/Hib) at 2, 3, 4 and 12 months of age. Both groups received concomitantly Prevnar 13 (PCV13) and Rotateq (RV5) at 2, 3 and 4 months of age and ProqQad (MMRV) at 12 months of age. MMRV was also administered to all study subjects at 13 months of age. RESULTS: A total of 628 subjects in the DTaP5-HB-IPV-Hib group and 622 subjects in the Control group were randomized. In a per-protocol analysis, immune responses to vaccine antigens 1 month after dose 3 and after the toddler dose were noninferior in the DTaP5-HB-IPV-Hib group as compared with the Control group. The DTaP5-HB-IPV-Hib group responses to MMRV given concomitantly at 12 months were all noninferior compared with the Control group. Solicited adverse event rates after any dose, including fever, were similar in both groups. Most adverse events were mild-to-moderate and did not lead to subject withdrawal. Vaccine-related serious adverse events occurred infrequently in the DTaP5-HB-IPV-Hib group (0.3%) and the Control group (0.2%). CONCLUSIONS: The safety and immunogenicity of DTaP5-HB-IPV-Hib is comparable to Control when administered in the 2-month, 3-month, 4-month and 12-month schedule. DTaP5-HB-IPV-Hib has the potential to provide a new hexavalent option for pediatric combination vaccines, aligned with recommended immunizations in Europe.

Heterogeneity of Rotavirus Vaccine Efficacy Among Infants in Developing Countries.

BACKGROUND: Rotavirus is the leading cause of severe diarrhea worldwide in young children. Although rotavirus vaccine efficacy is high in developed countries, efficacy is lower in developing countries. Here, we investigated heterogeneity of rotavirus vaccine efficacy by infant characteristics in developing countries. METHODS: An exploratory, post hoc analysis was conducted using randomized controlled trial data of the pentavalent rotavirus vaccine (RV5) conducted in Africa and Asia (NCT00362648). Infants received either 3 doses of vaccine/placebo and were followed for up to 2 years. Within subgroups, vaccine efficacies and 95% confidence intervals (CIs) against rotavirus gastroenteritis (RVGE) were estimated using Poisson regression. We assessed heterogeneity of efficacy by age at first dose, gender, breastfeeding status and nutrition status. RESULTS: African children receiving the first dose at <8 weeks had lower efficacy (23.7%; 95% CI: -8.2%-46.3%) than those vaccinated at ≥8 weeks (59.1%; 95% CI: 34.0%-74.6%). Marginally statistically significant differences were observed by age at first dose, gender and underweight status in Ghana and gender in Asian countries. CONCLUSIONS: Heterogeneity of efficacy was observed for age at first dose in African countries. This was an exploratory analysis; additional studies are needed to validate these results.

A Phase III randomized, double-blind, clinical trial of an investigational hexavalent vaccine given at 2, 4, and 11-12 months.

BACKGROUND: Combination vaccines simplify vaccination visits and improve coverage and timeliness. DTaP5-HB-IPV-Hib is a new investigational, fully-liquid, combination vaccine designed to protect against 6 infectious diseases, including 5 pertussis antigens and OMPC instead of PT as conjugated protein for Hib component. METHODS: In this multicenter, double-blind, comparator-controlled, Phase III study (NCT01480258) conducted in Sweden, Italy, and Finland, healthy infants were randomized 1:1 to receive one two immunization regimens. The DTaP5-HB-IPV-Hib Group received the investigational hexavalent vaccine (DTaP5-HB-IPV-Hib) and the Control Group received Infanrix-hexa (DTPa3-HBV-IPV/Hib) at 2, 4 and 11-12months of age. Both groups received concomitantly Prevnar 13 (PCV13) and Rotateq (RV5) or Rotarix (RV1) at 2, 4months of age and PCV13 at 11-12months. Subjects administered RV5 received a 3rd dose at 5months of age. RESULTS: A total of 656 subjects were randomized to the DTaP5-HB-IPV-Hib Group and 659 subjects to Control Group. Immune responses to all vaccine antigens post-toddler dose were non-inferior in the DTaP5-HB-IPV-Hib Group as compared to the Control Group. Additionally, the post-dose 2 and pre-toddler DTaP5-HB-IPV-Hib anti-PRP responses were superior. The DTaP5-HB-IPV-Hib Group responses to concomitant RV1 were non-inferior compared to the Control Group. Solicited adverse event rates after any dose were similar in both groups, except for higher rates of pyrexia (6.4% difference; 95% CI: 1.5,11.3) and somnolence (5.8% difference; 95% CI: 1.7,9.8) in the DTaP5-HB-IPV-Hib Group. Vaccine-related serious adverse events occurred infrequently in the DTaP5-HB-IPV-Hib Group (0.3%) and the Control Group (0.5%). CONCLUSIONS: The safety and immunogenicity of DTaP5-HB-IPV-Hib is generally comparable to Control when administered in the 2, 4, 11-12month schedule. Early Hib responses were superior versus Control. DTaP5-HB-IPV-Hib could provide a new hexavalent option for pediatric combination vaccines, aligned with recommended immunizations in Europe. STUDY IDENTIFICATION: V419-008 CLINICALTRIALS.GOV identifier: NCT01480258.

On analysis of longitudinal clinical trials with missing data using reference-based imputation.

Reference-based imputation (RBI) methods have been proposed as sensitivity analyses for longitudinal clinical trials with missing data. The RBI methods multiply impute the missing data in treatment group based on an imputation model built using data from the reference (control) group. The RBI will yield a conservative treatment effect estimate as compared to the estimate obtained from multiple imputation (MI) under missing at random (MAR). However, the RBI analysis based on the regular MI approach can be overly conservative because it not only applies discount to treatment effect estimate but also posts penalty on the variance estimate. In this article, we investigate the statistical properties of RBI methods, and propose approaches to derive accurate variance estimates using both frequentist and Bayesian methods for the RBI analysis. Results from simulation studies and applications to longitudinal clinical trial datasets are presented.

Evaluation of program success for programs with multiple trials in binary outcomes.

A late-stage clinical development program typically contains multiple trials. Conventionally, the program's success or failure may not be known until the completion of all trials. Nowadays, interim analyses are often used to allow evaluation for early success and/or futility for each individual study by calculating conditional power, predictive power and other indexes. It presents a good opportunity for us to estimate the probability of program success (POPS) for the entire clinical development earlier. The sponsor may abandon the program early if the estimated POPS is very low and therefore permit resource savings and reallocation to other products. We provide a method to calculate probability of success (POS) at an individual study level and also POPS for clinical programs with multiple trials in binary outcomes. Methods for calculating variation and confidence measures of POS and POPS and timing for interim analysis will be discussed and evaluated through simulations. We also illustrate our approaches on historical data retrospectively from a completed clinical program for depression.

Evaluating the adaptive performance of flexible sample size designs with treatment difference in an interval.

In clinical trials, the study sample size is often chosen to provide specific power at a single point of a treatment difference. When this treatment difference is not close to the true one, the actual power of the trial can deviate from the specified power. To address this issue, we consider obtaining a flexible sample size design that provides sufficient power and has close to the 'ideal' sample size over possible values of the true treatment difference within an interval. A performance score is proposed to assess the overall performance of these flexible sample size designs. Its application to the determination of the best solution among considered candidate sample size designs is discussed and illustrated through computer simulations.

Confidence intervals for an exposure adjusted incidence rate difference with applications to clinical trials.

To summarize safety data such as clinical adverse experiences in clinical trials with a moderate to long-term follow-up, we may use a measurement which accounts for the potential differences in the follow-up duration between treatment groups. The incidence rate, which uses the total person-time follow-up in a treatment group as the denominator, is one of these measures. When treatment comparisons are based on the difference of the incidence rates, it is of interest to construct confidence intervals for the rate differences. In this paper, we first discuss the assumptions and scenarios in which the exposure adjusted incidence rate may be appropriate. Then we review several methods of calculating confidence intervals for the difference of two incidence rates assuming that the number of events come from a Poisson distribution. The methods considered include Wald's method, the two-by-two table method, the Miettinen and Nurminen (MN) method, and the conditional MN method. For all but the MN method, explicit confidence intervals can be obtained. For the MN method, some numerical iterations are required. The properties of these methods are evaluated by simulations. The results show that the MN method outperforms the other three in terms of the coverage of the confidence interval, especially when the rates and therefore the number of events are small. Lastly, data from a clinical study are used to demonstrate the application of the methods.