How to use: work top to bottom. Step 1 gets the LRV of a single step from its load and output virus titers. Step 2 adds each unit operation (low pH, nanofiltration, AEX...) and its LRV to build the full train. Step 3 reads the cumulative LRV and the ICH Q5A pass/fail verdict on the right.
1Single-Step LRV Calculator
Titer Unit
Below LOD? ?
Load Titer (TCID50/mL)
Load Volume (mL)
Output Titer (TCID50/mL)
Output Volume (mL)
Limit of Detection (LOD) (TCID50/mL)
5.02
Single-Step LRV
2Multi-Step Clearance Builder
Add Step from Preset
Virus Model
Regulatory Target
Custom Target LRV
3Cumulative Clearance
0.00
Cumulative LRV
0 clearance steps
-
12.0
Target LRV
-12.0
Margin
0
Orthogonal Steps
Live Clearance Cascade
Virus in harvest109 / dose
—
Virus surviving to final product
—
Cumulative clearance
Each gate thins the swarm in proportion to its LRV for the selected model virus. Steps that are ineffective against this virus (e.g. low pH on a non-enveloped parvovirus) fade out and let particles through. Any survivors that reach the vial are what a patient would be exposed to.
LRV per Step
Add clearance steps to see the chart
Cumulative vs Target
020 LRV
Virus Model Panel Reference
Virus
Family
Envelope
Size (nm)
Genome
Key Resistance
MuLV
Retroviridae
Enveloped
80-110
RNA
Sensitive to low pH, S/D
X-MuLV
Retroviridae
Enveloped
80-110
RNA
Sensitive to low pH, S/D
MMV
Parvoviridae
Non-enveloped
18-24
DNA
Resistant to low pH, S/D, heat
PRV
Herpesviridae
Enveloped
120-200
DNA
Sensitive to low pH, S/D
Reo-3
Reoviridae
Non-enveloped
60-80
dsRNA
Moderate resistance
SV40
Polyomaviridae
Non-enveloped
40-45
DNA
Resistant to low pH, S/D, heat
Step Effectiveness by Virus Type
Clearance Step
MuLV
MMV
PRV
Reo-3
SV40
Mechanism
Low pH Hold
3-6
0-1
3-5
0-1
0-1
Inactivation
Protein A
1-3
1-2
1-3
1-2
1-2
Removal
AEX (flow-through)
3-5
3-4
3-5
3-4
3-4
Removal
CEX (bind/elute)
2-4
2-3
2-4
2-3
2-3
Removal
Nanofiltration (20nm)
>6
>4
>6
>5
>4
Removal
S/D Treatment
>5
0
>5
0
0
Inactivation
UVC Irradiation
2-4
2-3
2-4
2-3
2-3
Inactivation
Report Summary
#
Step
Virus Model
Load Titer
Output Titer
LRV
Cumulative LRV
Add clearance steps to generate the report
Frequently Asked Questions
What is a Log Reduction Value (LRV) in viral clearance?
A Log Reduction Value (LRV) quantifies the effectiveness of a viral clearance step. It is calculated as LRV = log10(virus load before step / virus load after step). An LRV of 4 means the step removed 99.99% of the virus. LRVs from individual steps are summed to obtain the cumulative clearance for the entire process.
What does ICH Q5A require for viral clearance in biologics?
ICH Q5A (Viral Safety Evaluation of Biotechnology Products Derived from Cell Lines of Human or Animal Origin) recommends that manufacturers demonstrate robust viral clearance through multiple orthogonal steps. For retroviruses and retrovirus-like particles from CHO cells, a cumulative clearance of 12–18 log10 or greater is generally expected. The guideline requires at least two robust, orthogonal (mechanistically different) clearance steps.
Which model viruses are used in viral clearance studies?
Common model viruses include: MuLV (murine leukemia virus) as a model for endogenous retroviruses; MMV (minute virus of mice) representing small non-enveloped parvoviruses (hardest to clear); PRV (pseudorabies virus) for large enveloped DNA viruses; Reovirus type 3 (Reo-3) for non-enveloped RNA viruses; and SV40 for non-enveloped polyomaviruses. The selection covers a range of sizes, structures, and resistance profiles.
How is LRV calculated when virus is below the limit of detection?
When no virus is detected in the output, the LRV is reported as a “greater than or equal to” value. It is calculated as LRV ≥ log10((load titer × load volume) / (LOD × output volume)), where LOD is the limit of detection of the assay. This gives a minimum clearance value and is typically noted with a “≥” symbol in regulatory submissions.
What is the difference between virus inactivation and virus removal?
Virus inactivation renders viruses non-infectious without physically removing them (e.g., low pH hold, solvent/detergent treatment, UVC irradiation). Virus removal physically separates viruses from the product (e.g., nanofiltration, chromatography). ICH Q5A recommends including both inactivation and removal steps to provide orthogonal clearance mechanisms.
Why is MMV (Minute Virus of Mice) considered the hardest virus to clear?
MMV is a small (18–24 nm), non-enveloped parvovirus that is extremely resistant to inactivation by low pH, heat, and solvent/detergent treatment. Its small size makes it challenging to remove by nanofiltration unless 20nm or smaller filters are used. Because of these properties, MMV represents a worst-case scenario for viral clearance validation and is included in most clearance studies.
What are typical log reduction values (LRV) by clearance mechanism?
Low-pH viral inactivation typically achieves ~3–6 LRV for enveloped viruses (e.g. retro/MuLV) but near 0 for resistant non-enveloped viruses, while anion-exchange (AEX) flow-through gives ~3–5 LRV across many virus types. Protein A capture is usually credited only ~1–2 LRV and is not claimed as a robust step, whereas small-virus (parvovirus) nanofiltration at ~20 nm delivers >4 LRV. Regulators expect at least two orthogonal effective steps, with overall targets often 12–18+ LRV for the retrovirus model.