Classifications of Viruses: Biological Risk Assessment

February 18, 2022
Classifications of Viruses: Biological Risk Assessment


  1. What Is A Virus?
  2. The Evolution of Viruses
  3. How Small Are Viruses?
  4. Types Of Viruses
  5. What Are The Risk Assessment Steps?
  6. Viral Risk Assessment Classifications
  7. Final Thought


As the COVID-19 pandemic started to unravel, there was an extensive risk assessment was conducted by scientists that determined its rate of transmission and risk to public health. Biological risk assessment is one of the key principles of biosafety. It is the process used to identify the hazardous characteristics of an infectious organism, the activities that could lead to exposure, the chances of contracting a disease after exposure, and the consequences of an infection. Risk assessment provides the necessary information to determine the appropriate biosafety measures (facility characteristics, microbiological practices, safety equipment, etc.)

Continue reading further to learn more.


A virus is a small collection of genetic code, either DNA or RNA, surrounded by a protein coat. A virus cannot replicate alone. As a result, viruses must infect cells and use components of the host cell to make copies of themselves. Often, they kill the host cell in the process and cause damage to the host organism. Researchers estimate that viruses outnumber bacteria by 10 to 1. Because viruses don’t have the same components as bacteria, they cannot be killed by antibiotics. Only antiviral medications or vaccines can eliminate or reduce the severity of viral diseases, including AIDS, COVID-19, measles, and smallpox.


Although biologists have accumulated a significant amount of knowledge about how present-day viruses evolve, much less is known about how viruses originated in the first place. When exploring the evolutionary history of most organisms, scientists can look at fossil records and similar historical evidence. However, viruses do not fossilize, so researchers must conjecture by investigating how today’s viruses evolve and by using biochemical and genetic information to create speculative virus histories.

While most findings agree that viruses don’t have a single common ancestor, scholars have yet to find one hypothesis about virus origins that is fully accepted in the field. One possible hypothesis, called devolution or the regressive hypothesis, proposes to explain the origin of viruses by suggesting that viruses evolved from free-living cells. However, many components of how this process might have occurred are a mystery. As technology advances, scientists may develop and refine further hypotheses to explain the origin of viruses.


Viruses are submicroscopic, which means that you cannot see them under the microscope. What’s interesting about viruses is that they have two or three components. Starting from the inside, you will have a nucleic acid, which can be either RNA or DNA, and in both cases, the nucleic acid can be either single-stranded or double-stranded. Then surrounding the nucleic acid will be a protein coat that’s in the form of a capsid or little small units that are assembled in a certain way. That is what all viruses have.

Now, some viruses will also have an envelope that they obtain as they emerge from the cell. Viruses are very interesting in that they can only survive inside a living cell. So they must have a living cell to survive and replicate.


The three primary types of viruses are:

  • Helical: The virus consists of nucleic acid enveloped by a hallow protein cylinder or capsid that has a helical shape. (Ex: Tobacco mosaic virus)
  • Envelope: The virus is covered with a modified section of the cell membrane, a protective lipid envelope. (Ex: Coronavirus, HIV, and Influenza)
  • Icosahedral: The virus is nearly spherical in shape. (Ex: Polio, Rhinovirus, and Adenovirus)
  • Complex: Resemble a lunar lander, and are composed of a polyhedral head, helical body, and legs that attach to a cell membrane. (Ex: Poxvirus and Geminvirus)


In general, risk assessments can be broken down into a 2-step process. The risk assessment often includes consideration about the hazards (e.g., biological agent), the specific processes and procedures, existing control measures, the facility and testing environment, and the competency of the testing personnel.

  • Identify the Hazards and Risks
    • What, where, and how is the work occurring?
    • Who is involved in the work?
    • What can go wrong?

For a specific activity or procedure, identifying the hazards in each step or task must be completed amongst virologists. Ask what, where, and how the work is occurring and who is doing the work. Then, virologists determine what could go wrong in every step of the activity or procedure and the result of the undesirable incident (e.g., injury, exposure, infection, disease).

  • Evaluate the risk
    • How likely is the risk and how severe is it?
    • Is the risk acceptable or unacceptable?

There are various and multiple risks involved in performing laboratory testing. It is important for risk assessments to evaluate each risk against a standard set of criteria so that the assessed risks can be compared against each other. The criteria focus on both the likelihood of the undesirable incidents occurring and the consequences of these incidents were to occur.


The U.S. Department of Health and Human Services (HHS), Center for Disease Control and Prevention (CDC), National Institutes of Health (NIH), Food and Drug Administration (FDA), Biomedical Advanced Research and Development Authority (BARDA), and Department of Defense (DoD) focuses on the rapid characterization of emerging variants and actively monitors their potential impact on critical countermeasures, including vaccines, therapeutics, and diagnostics.

Given the continuous evolution of a virus, such as the SARS-CoV-2, and its impact on public health, variants may be reclassified based on their attributes and prevalence in the United States.

  • Variants being monitored (VBM): less than 1 case per 100,000 people
  • Variant of interest (VOI): 1-9 cases per 100,000 people
  • Variants of Concern (VOC): 10-24 cases per 100,000 people
  • Variant of high consequence (VOHC): 25+ cases per 100,000 people


Viruses are biological entities that are present in all living beings. Some are harmless, while others can cause a range of diseases, from the common flu to COVID-19. One certain thing is the essential role viral risk assessment plays in determining the risk factors and safety precautions. Seeking protection from potentially hazardous viruses — for example, through vaccinations — can help prevent serious illness.

Did you get your COVID-19 vaccinations yet? What did you think of the article? Was there anything else you would like to know more about? Feel free to leave us a comment below.

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