Validation Strategy of Viral Decontamination Methods, a quick overview


Even though much progression has occurred in terms of quality and compliance in the biopharmaceutical environment, the industry is still mired in vague definitions of « decontamination » very often leading to amalgams with the actions of « cleaning » and « disinfection ».

This confusion, particularly in the bio-pharmaceutical realm of infectious antigens and particularly viruses, leads to situations of non-technical mastery, non-compliance and ultimately increased risk of cross contamination between products. All of which stress the importance of clarity in biocontainment.

In the early 2000’s, due to external pressures, the industry was obliged to remove formalin (CMR) which was widely used as a decontamination reagent. Adopting alternative decontamination reagents highlighted three main points: (i) historical decontamination exposed the relative ineffectiveness of formalin in the light of current practices; (ii) validating the performance efficiency of decontaminants is difficult (too many external variable factors influencing its performance); (iii) highlighted the need for in depth performance review of all the tools and decontamination processes. These observations are further supported by Polio eradication ambitions conducted by WHO (GAP-III) which also highlighted these gaps and weaknesses.

Nowadays, associated technologies of different decontamination methods (i.e., Physics, Thermal, Chemical) are numerous, and provide a wide panel of choices that can be employed in the biopharmaceutical industries, and especially vaccines companies. Accordingly, the duty of mastery and performance validation of decontamination processes is no longer an option (!) However, new constraints are emerging and require substantial human and technical resources impacting the project costs, perhaps exponentially running into millions of euros!

This article aims to serve as a “lessons learned” and is on based many years of alternative decontamination investigations. The article also shares the strategy, initially conceived in 2004, that was designed to anticipate the new paradigm of state of the art of decontamination. Finally this article aims to participate in the education on this often misunderstood and often over looked topic…


It is important to clarify the pharmaceutical definitions of « cleaning » and « disinfection », and further elucidation can be highlighted by examples.

Result of an operation in a limited time, allowing the withdraw of all undesirable inert compounds acquired on contaminated surfaces according to laid down objectives. The result of this operation is limited to the compounds being present at the time of the operations.
These compounds come from natural environmental sources or from the product handled.
Objectives aimed by CLEANING are inert compounds (Production or laboratory‘s areas)

Result of an operation in a limited time, allowing the withdraw, inactivation or killing all undesirable micro-organisms carried by contaminated inert media according to laid down objectives. The result of this operation is limited to the micro-organisms being present at the time of the operations (AFNOR NFT 72-101).
These micro-organisms are not specific and come from natural environmental sources.
Objectives aimed by DISINFECTION are the environmental microorganisms (Production or laboratory‘s areas).

The definition of decontamination can flow from the two previous ones:
Result of an operation in a limited time, allowing inactivating, killing or destroying all specific micro-organisms handled according to laid down objectives. These micro-organisms are known and specific.
Objectives aimed by
DECONTAMINATION are to control of the dissemination of the specific micro-organisms (vaccine products or microorganisms handled in laboratory)

In conclusion, the use of the disinfection term as a synonym of decontamination has to be prohibited. Finally Cleaning does not insure disinfection or decontamination. Similarly, disinfection does not insure decontamination or cleaning.


Strategy of viral decontamination
Considering all of the decontamination technologies (physical techno’s, chemical reagents…) with differing mechanisms, that we will call the “Weapons” (see tables 1 & 2) coupled with the huge number of viruses, that we will call the “Targets” , the list of validations to perform may become unmanageable, lengthy and cost prohibitive.

Chemical modes
Liquids reagents In depth and/or surface decontamination
Gaseous Mainly surface decontamination
Physical modes
Radiation In depth and surface decontamination
(pulsed) Light In depth and/or surface decontamination
e-beam (mainly) Surface decontamination
Thermal modes Mainly used for depth decontamination
(Autoclaves, Oven)

Table 1: Decontamination modes, that we will call the “Weapons”

Fortunately, viruses elicit interesting properties such as (i) Their inability to generate resistant mutation against chemical reagents (because resistant mutation occurrence can only be acquired during their viral replication which is not the case here) (ii) Their composition with 4 basic compounds, Nucleic acids, Amino acids, sugars and lipids which essentially transform viruses in to simple chemical targets rather than “daunting” viruses.

Considering these new paradigms of viral properties, possibilities emerge including a “bracketing strategy” to create virus models representing the worst case scenarios. Obviously, the rule of bracketing can’t generalized absolutely, but can be linked to a clear and a strong scientific rational, a list of specific criteria’s and also linked to a list of considered viruses. In the following example, 9 viruses routinely handled in a vaccine company will be analyzed (table 3).

After having identified the targets and the weapons, all the “Constraints” should be identified.

From the targets side:
The availability of the target (i.e.: level of concentration, fragility of microorganisms…), the availability of lab’s capability for handling (biosafety containment), the availability of the Methods of quantification: are they available, if yes what are their detection limits, their robustness(matrix viro and/or cytotoxicity)?

Modes / Reagents Main Target(s) on viral structure
Temperature Viral envelop, (Glyco)protein’s , RNA then DNA
Acids / Bases Viral envelop, (Glyco)protein’s
Alcohols / Ether Viral envelop, (Glyco)protein’s
(Cl- , O3, H2O2, formalin, b-propiolactone…)
Viral envelop, (Glyco)protein’s, Nucleic Acids
Detergents (ionic / nonionic) Viral envelop
UV / p-Light Nucleic Acids, (Glyco)protein’s

Table 2: Decontamination modes versus biochemical viral elements: impact on viral structure

From the Weapons side:
Are chemical reagent’s compositions available? (i.e. nature and concentration of each component)? Are corresponding neutralizing reagents available? What is their Impact on methods of quantification due to cytotoxicity?
Because of the target constraints (susceptibility, level of concentration, expression systems…), one of strategies is to bracket the microorganisms to define the best model which will be able to cover a maximum number of them and will allow defining the efficient decontamination parameters. The microorganism model selected must be derived from minimally 3 main criteria (i) a Risk Analysis with the well-defined rules of bracketing. (ii)The physical availability of the potential microorganism’s model including the infectious titer level compatible with the final objectives, and iii) the method of quantification used (lower detection limit, Its accuracy at low level, robustness…).
Aware of all these key elements, the efficiency specifications should be set up. Unfortunately clear and exhaustive regulatory guidance are lacking (French, European, US, International ones…) and if provided, is limited and do not cover all the cases, especially for viruses(Table 4). Regarding each decontamination mode, the regulatory specifications are not so clear and often derived from sterility assurance experiences, such as the famous “6 Log reduction”.

Specifically for viral targets, one can find 4 log reduction of infectious titer using chemical mode, but in most of the viral cases, it is not appropriate. This leads us to the following questions what are the right specifications for (i) Surface decontamination, (ii) Liquid waste, (iii) solid waste, (iv) air? Without this guidance, a bibliography study is needed at least.
Most of the time, the efficient parameters claimed on the label for ready to use decontamination products are not appropriate because of a vast absence of methodological information like environmental conditions, scientific approach and minimal of performance requirements (i.e. 4 Log reduction linked to a norm…)

Structural Composition
Viruses External Spikes : glycoprotein Envelope :
Core : protein Genus : ARN Conclusions following the “bracketing strategy” rules
Poliovirus (Enterovirus) No No Yes Yes Viruses into group 1
Model represented by Poliovirus
Hepatitis A (Enterovirus) No No Yes Yes
Influenza virus (Flu) Yes Yes Yes Yes Viruses into group 2

Model represented by Influenza virus
Measles (Morbilivirus) Yes Yes Yes Yes
Mumps virus (Rubulavirus) Yes Yes Yes Yes
Rubella virus (Rubivirus) Yes Yes Yes Yes
Rabies virus (Lyssavirus) Yes Yes Yes Yes
Y-Fever (Flavivirus) Yes Yes Yes Yes
Dengue (Flavivirus) Yes Yes Yes Yes

Table 3: List of 9 considered viruses, that we will call the “Targets”
Based on biochemical structure of each virus, here we can define 2 models, according to the following characteristics and the “constraints” which were identified in the specific rules set up


Finally the Strategies of Validation can be summarized as such: The right weapon against the right target with the best tool box, which should be defined specifically. In any case, all (your) the specifications must be set up in regards of each specific use.

 Specifications of chemical liquid decontamination
 Bactericide French Norm AFNOR NF T 72-170 and 171 5 Log reduction
European Norm NF EN 1040
Sporicide French Norm AFNOR NF T 72-230 and 231 5 Log reduction
Fungicide  French Norm AFNOR NF T 72-200 and 201 4 Log reduction
European Norm NF EN 1275
Virucide  French Norm AFNOR NF T 72-180, 181 and 185 4 Log reduction
European Norm NF EN, 14675/14476 and 13610

Specifications for chemical air decontamination

Bactericide  5 Log reductionSporicide French Norm AFNOR NF T 72-2813 Log reductionFungicide  4 Log reductionVirucide  4 Log reduction
(New! Nov.14)

Table 4: examples of norms for specification setting up

After more than 10 years’ experience, our lesson learned has provided valuable positive experience. All (our) viruses are linked to their validated efficient decontamination parameters, in a compliant, coherent and robust system while realizing savings via our approach. Now each new potential decontamination reagent is easy to validate and a comprehensive update to our decontamination system for all viruses in can be performed in a few experiments. Moreover, the strategy has been vetted with regulatory authorities resulting in increased compliance with no significant observations.

The remaining challenge, is to educate auditors who are not all familiar with viruses reducing their preconceived notions of viral complexity thereby enabling full endorsement of the performance and efficiency of these approaches and data.



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