John Muganga is senior manager, Regulatory Affairs at ICON plc.

John Muganga

Adeno-associated virus. AAV virus genome. Adenoviral pneumonia, arthritis, bronchitis, hepatitis, cystitis. Adenovirus as vectors for gene therapy. Genetic material transmission to cell. Biotech 3D | Image Source: ©Corona Borealis -stock.adobe.com

The 2024 implementation of the International Council for Harmonisation’s (ICH) Q5A(R2)

guideline marks a substantive evolution in viral safety for biotechnology products since the last iteration was published in 1997. This guidance supports more risk‑based, technology‑enabled controls that keep pace with modern modalities, manufacturing models, and technologies.

The revision formalizes the role of molecular methods, notably next-generation sequencing (NGS), for broad adventitious agent detection and encourages judicious replacement of legacy in vivo assays. It also addresses continuous manufacturing, platform prior‑knowledge, and new product modalities where viral clearance is demonstrably feasible.

This article explores practical actions for manufacturing and chemistry, manufacturing, and controls (CMC) teams to align with Q5A(R2)’s updated guidance and stay ahead of the rapidly changing viral safety environment. Implemented well, these actions can shorten testing timelines and strengthen assurance of participant safety.

Q5A(R2) revisions that CMC teams should take specific notice of are the following:

Molecular methods mainstreamed: Q5A(R2) formalizes the role of nucleic‑acid methods, especially NGS, for broad adventitious agent detection in cell banks and unprocessed bulk, with a risk‑based path to replace certain legacy in vivo tests.

Continuous manufacturing (CM): A new section details how to evidence viral clearance when operations run for extended durations with pooling and diversion.

Prior knowledge and new modalities: The guideline clarifies when platform experience can reduce study scope and explicitly covers modalities amenable to clearance (eg, adeno-associated virus [AAV] produced in cell lines, baculovirus‑expressed virus-like particles [VLPs]).

Q5A(R2) expects sponsors to build and justify a risk-based viral safety from overlapping controls: what you prevent from entering the process, what the process removes or inactivates, and what you verify through testing at defined steps.

Start with a simple risk narrative that spans cell substrate → raw materials → upstream → downstream → drug substance. For each link, decide whether control comes from testing, from clearance, or both. Maintain the classic triad of cell line and materials control, process clearance, and testing at appropriate steps, but tie claims to critical quality attributes (CQAs), critical process parameters (CPPs), and a representative small‑scale model.

Q5A(R2) supports reduced product-specific work when prior knowledge is robust, and the rationale is evidence-backed. Define clear platform boundaries (process architecture, materials, operating ranges), explain mechanisms (inactivation vs removal), and bridge with historical data under worst case CPPs. The revised guidance offers worked examples (low pH, solvent/detergent [S/D], filtration) sponsors can use as a template for required structure and depth. When properly supplemented with prior knowledge dossiers, testing timelines may be reduced. 

NGS in Practice: Where It Replaces vs Supplements

NGS is a vital part of an integrated control strategy alongside traditional in vivo and in vitro assays and clearance validation. It offers broad, agnostic detection even for variants and potential novel viruses, making it a credible alternative to some targeted assays. However, NGS detects nucleic acid, not infectivity. As such, dossiers need an orthogonal confirmation plan and a validation package that matches the claim, whether that’s breadth vs sensitivity, targeted vs non‑targeted workflows, database governance, bioinformatics controls, etc.

A pragmatic path forward with NGS is first to supplement then replace. Piloting NGS alongside established assays and demonstrating concordance builds evidence to justify replacement where risk and data allow. Industry feedback during the Q5A(R2) consultation and subsequent implementation guidance emphasize the need to define intended use, detection limits in relevant manufacturing matrices, and the application of expert curation of bioinformatic results.

Demonstrable Clearance in Continuous Manufacturing

In CM, viral clearance shifts from one-time proof to demonstrating its reliability across a continuously operating system so that viral risk remains controlled across time, variability, and scale.

Demonstrable clearance requires sponsors to position low-pH inactivation, dedicated virus inactivation (VI) steps, chemistry where applicable and nanofiltration so they bound risk; define material segmentation, diversion, and pooling rules; and prove the scale‑down model remains representative over the intended run duration to support viral clearance claims. Sampling plans should align with segmentation, not just hours of operation, to ensure samples represent a single, clearly defined lot or batch.

The following plant-ready viral safety 2.0 checklist can be used to confirm that viral safety controls are clearly defined, evidence-based and ready for routine manufacturing use:

Map controls end‑to‑end and keep the map in change control (cell banks, raw materials, holds, unit ops, sampling points).

Define plain‑language clearance claims and link each to CQAs/CPPs, scale‑down evidence, and routine monitoring.

Harden raw‑material governance: origin, treatments (eg, irradiation/filtration), and risk‑ranked incoming controls.

If deploying NGS, lock down sample handling, sequencing depth, database curation, and a bioinformatics validation plan—with expert review and an orthogonal confirmation playbook.

For CM, pre‑define segmentation/pooling logic and time‑at‑risk bounds; align sampling to segments.

Build a modular prior‑knowledge library per unit operation and maintain applicability limits and data currency.

Q5A(R2) makes viral safety transparent and risk‑based, supported by modern analytics and demonstrable clearance. Understanding the guidance’s revisions and how to implement them creates opportunities for accelerated testing timelines, stronger safety assurances, and the integration of next-generation innovations.

Q5A(R2) Guideline on viral safety evaluation of biotechnology products derived from cell lines of human or animal origin: scientific guideline—Step 5

. EMA/CHMP/ICH/804363/2022. Adopted December 2023. Effective June 14, 2024. Accessed April 20, 2026.

International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use. 

ICH Q5A(R2) Implementation Working Group concept paper

. December 2023. Accessed April 20, 2026.

Articles

ICH Q5A(R2) modernizes viral safety expectations for biotech products by shifting toward risk-based, technology-enabled controls aligned with contemporary modalities and manufacturing paradigms. Molecular methods, particularly next-generation sequencing, are formalized for broad adventitious agent detection, enabling potential retirement of select legacy in vivo assays when justified. The guidance expands considerations for continuous manufacturing, emphasizing demonstrable clearance over extended operations with defined segmentation and sampling logic. It also endorses structured use of platform prior knowledge to reduce product-specific studies when boundaries and evidence are robust.

CMC teams can align with Q5A(R2)’s updated guidance to shorten testing timelines and strengthen assurance of participant safety.