These potency tests should comply to strict validation criteria in terms of ac-

curacy, precision (repeatability, intermediate precision), specificity, linearity, limit

of detection and limit of quantitation, system suitability and robustness, in ac-

cordance with the ICH Q5A(R1) guideline [20].

4.4.3

MOLECULAR ASSAYS AND CONTROL OF THE VIRAL RISK IN THE FUTURE

A major complication in the control of the viral risk is the continued discovery of

new virus species/genera and variants, especially given the power of a new tech-

nology like NGS. This technology enables sequencing (i.e., identifying) millions of

nucleic acid molecules with known and unknown preliminary knowledge of their

sequences with unprecedented speed, quality, coverage, and depth.

The increasing number of newly identified viruses is illustrated in Figure 4.1. This

graph is based on the taxonomy releases between 1971 and 2020 in the ICTV

(International Committee on Taxonomy of Viruses) depository, in which the numbers

of new virus species, genera, and families were counted. The number of virus species

increased 2.5-fold between 2015 and 2020, from 3,704 to 9,110 (Figure 4.3).

The number of virus families, genera, and species are reported in historical ICTV

(International Committee on Taxonomy of Viruses) taxonomy releases.

The viral risk assessments and the associated mitigation strategies based on the

specific testing, such as PCRs, can become rapidly obsolete. New assays cannot be

systemically developed and implemented after each new virus/variant discovery.

In addition, like other molecular-based assays, PCR and NGS cannot discriminate

between nucleic acid from non-viable and viable/replicative viruses. Indeed, both

methods can detect small DNA or RNA molecules which could be fragmented by

inactivation treatments such as gamma-irradiation. For example, in a study by Toohey-

Kurth et al. [41], NGS was used to analyze 26 bovine serum samples from 12 man-

ufacturers. Twenty viruses belonging to nine virus families were detected in this study.

Four viruses were taxonomically unassigned. The authors recognized that the presence

of viral nucleic acids did not indicate contamination with infectious virus.

FIGURE 4.3 Illustration of the increasing number of new viruses.

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Bioprocessing of Viral Vaccines