Abstract
From the perspective of vaccine development, it is imperative to accurately diagnose target infections in order to exclude subjects with prior exposure from evaluations of vaccine effectiveness, to track incident infection during the course of a clinical trial and to differentiate immune reactions due to natural infections from responses that are vaccine related. When vaccine development is accelerated to a rapid pace in response to emerging infectious disease threats, the challenges to develop such diagnostic tools is even greater. This was observed through the recent expansion of Zika virus infections into the Western Hemisphere in 2014–2017. When initial Zika vaccine clinical trials were being designed and launched in response to the outbreak, there were no standardized sets of viral and immunological assays, and no approved diagnostic tests for Zika virus infection. The diagnosis of Zika virus infection is still an area of active research and development on many fronts. Here we review emerging infectious disease vaccine clinical assay development and trial execution with a special focus on the state of Zika virus clinical assays and diagnostics.
Highlights
The declaration by the World Health Organization (WHO) that Zika is a public health emergency of international concern in February 2016 led to a global effort to support vaccine development and control the spread of Zika virus (ZIKV)
The diagnostic assay development response to ZIKV was quite rapid with the Emergency Use Authorization (EUA) approval of 14 different molecular detection assays and five serological assays in roughly 18 months’ time (Tables 1 and 2) and the initiation of efforts to build international reference standards for both assay types
While our understanding of the immune response to ZIKV has greatly expanded since the start of the most recent outbreak and leverages the years of vaccine research for other flaviviruses, such as dengue, there is still no established immune correlate of protection
Summary
The declaration by the World Health Organization (WHO) that Zika is a public health emergency of international concern in February 2016 led to a global effort to support vaccine development and control the spread of Zika virus (ZIKV). One of the clear gaps affecting both public health efforts and vaccine development programs was a lack of standardized reagents and methods to test for evidence of current or prior Zika infection. Expanding that concept to the public health scale and attaining accurate infectious disease diagnoses allows for better understanding of the course and severity of an outbreak and aids decision-making for population-level countermeasure implementation. The clinical assays with which the immune response and pathogen presence are measured in vaccine trials become part of the basis for licensure for all vaccine products [4]. Because vaccines are tested in healthy populations through all phases of clinical development for immune response and/or pathogen presence whereas drugs/biologics (post-Phase I) are most often tested in a population with specific disease to demonstrate improvement, the selected methods to measure vaccine responses and endpoints are of the utmost importance. Vaccines 2018, 6, 70 public health countermeasures for containment and vaccine development as an example of challenges faced during emerging infectious disease emergencies
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