Quality Control and Testing
May 26, 2022
| 5 min read

Common Challenges in Completing Virus Clearance Validation Studies

Virus clearance validation is essential for biopharmaceutical manufacturers using animal- or human-derived materials. Validation is unique to each process and thus not always easy in practice. Learn about common validation study challenges and how to avoid them to ensure good retention results for purification steps. 

This article is posted on our Science Snippets Blog

The risk of viral contamination is a serious concern for all biopharmaceutical products and vaccines that use human- or animal-derived materials because it poses serious safety risks to patients. The cost of contamination can also be very high to a manufacturer, requiring:  

  • Investigation
  • Clean-up
  • Corrective action
  • Manufacturing plant downtime

To prevent viral contamination, regulatory agencies require manufacturing processes to have a validated cGMP downstream purification process that can remove or inactivate a wide variety of viruses. Unfortunately, the validation processes are not always simple or clear. Avoiding common challenges means working with a partner that can help biopharmaceutical and vaccine manufacturers adhere to regulatory requirements and streamline validation.

Virus Clearance Validation Steps

Virus clearance studies are a regulatory requirement for any investigational new drug (IND) application and any biologics license application (BLA). These validation studies demonstrate whether a purification process can efficiently remove or inactivate viruses.  

Virus clearance requires three major steps:  

  • Pre-testing: This step ensures a reliable log reduction value (LRV) determination, with a TCID50 assay, for example. It includes cytotoxicity to evaluate the product’s toxicity to the indicator cells (ensuring that only the virus in question causes cellular damage) and viral interference testing to evaluate how well the product can inhibit viral infectivity.  
  • Main study: Lab analysts spike the product with a determined concentration of the virus, then perform the removal or inactivation step. Analysts take initial load samples and further process samples according to test protocols.
  • Reporting: Analysts compare the initial viral load to the viral load after the purification step, presenting a log10 reduction value of the determined reduction capabilities. An LRV greater than 4 shows efficient virus clearance.

Common Pitfalls of Virus Clearance Studies

Manufacturers may observe low LRV results in a virus clearance validation study even after extensive purification process planning and design. This is often the result of membrane fouling or small viruses' breakthrough. The most common causes are:

Buffer Conditions  

Based on the molecule’s characteristics, there are questions about the most suitable chemistry of a chromatography consumable. In a second step, suitable buffers for both the molecule but also the chromatography step must be chosen. Only the correct buffer choices will ensure good virus binding and product flow.


More is not always better. Overloading membrane adsorbers can lead to reduced binding capacity. Manufacturers should adjust loading capacity based on the number of expected impurities in each step—for example, the second chromatography step will have different impurity levels than the third step.

Virus filter overloading can cause pressure peaks and impact flow rates. This could lead to small virus breakthroughs and make it harder to achieve the target throughput.  

The only way to determine the actual capacity for a process is by analyzing different fractions taken during virus clearance validation.  

Product Aggregation & Virus Spike Purity 

Product aggregation has as much of a negative impact on validation studies as it does on the actual production process. Aggregation during validation studies can result from: 

  • Freeze and thaw process
  • Improper handling of shear-sensitive products  
  • Reactions between the product and the virus   

Pre-filters should always be part of a validation process set up to break up potential aggregations.  Furthermore, if the product is prone to aggregation, it is recommended that a trial run be performed prior to the actual study to identify any additional countermeasures that may be required.  

Virus purity is also of high interest. For example, a crude virus with still present cell debris or other unwanted impurities can quickly lead to membrane blocking. As with product aggregation, an adequate pre-filtration step is the best solution for virus purity.

Equipment Handling  

It is especially important to properly pre-wet membrane absorber devices on a small scale. Otherwise, virus retention results may exhibit high variability. In addition, manufacturers should use a pre-filter prior to the current purification step to remove air and particles that may cause pressure to rise.

These mistakes can lead to significantly higher costs from wasted product and delayed time to market while you investigate, and potentially must repeat studies. Mistakes can also trigger corrective action and other regulatory hurdles. In part two of this blog, we’ll focus on membrane absorbers and how a small-scale anion exchange membrane absorber can improve virus clearance studies, lower costs, and save time in your process.

The Fundamentals of Virus Clearance Studies

In this video, you will learn more about the basic principles of virus clearance studies. In addition, we introduce you to the most important aspects of conducting these studies at Sartorius and give you more details about our virus clearance service offering.

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