The Impact of Sparse Follow-up on Marginal Structural Models for Time-to-Event Data.

The impact of risk factors on the amount of time taken to reach an endpoint is a common parameter of interest. Hazard ratios are often estimated using a discrete-time approximation, which works well when the by-interval event rate is low. However, if the intervals are made more frequent than the observation times, missing values will arise. We investigated common analytical approaches, including available-case (AC) analysis, last observation carried forward (LOCF), and multiple imputation (MI), in a setting where time-dependent covariates also act as mediators. We generated complete data to obtain monthly information for all individuals, and from the complete data, we selected "observed" data by assuming that follow-up visits occurred every 6 months. MI proved superior to LOCF and AC analyses when only data on confounding variables were missing; AC analysis also performed well when data for additional variables were missing completely at random. We applied the 3 approaches to data from the Canadian HIV-Hepatitis C Co-infection Cohort Study (2003-2014) to estimate the association of alcohol abuse with liver fibrosis. The AC and LOCF estimates were larger but less precise than those obtained from the analysis that employed MI.

Quantitation of serogroups in multivalent polysaccharide-based meningococcal vaccines: optimisation of hydrolysis conditions and chromatographic methods.

Quantitative determination of the individual polysaccharide components in multivalent meningococcal vaccines is an important step in manufacturing and regulatory control. Current methods are complicated due to the use of multiple chromatographic setups and/or other analytical techniques for the four meningococcal serogroup polysaccharides (A, C, Y, W135). In addition, different methods are sometimes used depending on whether or not the polysaccharide is conjugated to a carrier protein. In an effort to simplify such analyses, hydrolysis conditions were determined for the optimal yield of each characteristic saccharide from the respective repeating units. One condition was identified for mannosamine-6-phosphate from MenA, one for neuraminic acid from MenC, and one for both glucose and galactose from MenY and MenW135, respectively. These conditions, initially assessed for monovalent solutions, were then confirmed for a quadrivalent solution. The monosaccharide products were separated, identified and quantitated using a single HPAEC-PAD protocol, with a customised multi-stage linear gradient eluent profile and one column setup, for determination of all four serogroup components. Comparison to calibration curves constructed from sets of monosaccharide or hydrolysed polysaccharide standards allowed for the quantitation of each characteristic serogroup monosaccharide in polysaccharide and polysaccharide-conjugate vaccines. When required, molecular size separation using a non-cellulosic centrifugal filter device effectively removed all interfering saccharide excipient without loss of serogroup polysaccharides. These methods were used to analyse multiple lots of a number of different monovalent or multivalent real polysaccharide-based vaccine products, in liquid or lyophilised powder formulations, with or without excipients. The methods were demonstrated to be highly reproducible and very useful for the evaluation of antigen content and lot-to-lot consistency of manufacture. The methods described here represent an increase in precision, level of accuracy and efficiency compared to current methods, and may be adaptable for evaluation of other types of polysaccharide-based vaccines.

Modifying the thermostability of inactivated influenza vaccines.

BACKGROUND: Respiratory infections caused by influenza viruses spread rapidly, resulting in significant annual morbidity and mortality worldwide. Currently, the most effective public health measure against infection is immunisation with an influenza vaccine matching the relevant circulating influenza strains. Although a number of developments in terms of influenza vaccine production, safety and immunogenicity have been reported, limitations in our understanding of vaccine stability still exist. In this report we seek to identify compounds that increase influenza vaccine thermostability. METHODS: We use plaque inhibition on confluent MDCK cells to identify compounds which inhibit the entry of various seed strain viruses. The effect of these compounds on vaccine thermal lability is evaluated through SRID analysis. The significance of these results is tested by a two-way analysis of variance (ANOVA) method. RESULTS: We identify two compounds which selectively inhibit entry of different group I or group II influenza strains through prevention of the neutral-pH to low-pH conformational change of hemagglutinin. Compounds which were able to inhibit virus entry were also able to limit thermally induced potency loss in matched influenza vaccines. Furthermore, we demonstrate that this effect is independent of product formulation or the presence of multiple HA types. CONCLUSIONS: This work provides further evidence for a link between HA conformational stability in the virus and thermostability of the corresponding vaccine preparation. It also suggests straightforward approaches to improve the stability and predictability of influenza vaccine preparations.

Bioactivity determination of native and variant forms of therapeutic interferons.

The traditional antiviral assays for the determination of interferon potency are reported to have considerable variability between and within assays. Although several reporter gene assays based on interferon-inducible promoter activities have been reported, data from comprehensive validation studies are lacking and few studies have been conducted to analyze the variant forms of interferons, which could have undesirable clinical implications. Here, a reporter gene assay employing a HEK293 cell line stably transfected with luciferase gene under the control of interferon-stimulated response element promoter was developed and validated. The assay was found to be more sensitive, with a larger detection range than the antiviral assay. Several cytokines tested did not interfere with the test, suggesting the assay possesses a certain degree of selectivity. Moreover, the robustness of the assay was demonstrated by minimal variations in the results generated by different analysts and cell passage number (up to 52 passages). Finally, the method was employed to analyze several interferon variants (interferon-α 2a) and we found that the aggregated form has completely lost its potency; while a modest loss of bioactivity in oxidized interferon was observed (approx. 23%), the deamidated form essentially retained its activity.

Modified binding assay for improved sensitivity and specificity in the detection of residual pertussis toxin in vaccine preparations.

A binding assay was recently published that differentiates between pertussis toxin (PTx) and the pertussis toxoid (PTd) used in acellular pertussis vaccines based on the selective binding of PTx to fetuin and detection with a polyclonal antibody. We found that the assay specificity for PTx was affected by both pH and salt. A monoclonal antibody (mAb) was identified that eliminated specificity problems and improved the sensitivity to 0.4 ngPTx/ml. This mAb was previously shown to neutralize PTx toxicity in vivo, thereby supporting the assay's potential biological relevance as an alternative to the mouse histamine sensitivity test for the safety of pertussis vaccines.