Poxvirus and Poxviral Vectors

Poxviruses are enveloped, double-stranded DNA viruses that carry out their life cycle within the cytoplasm of the infected cell.  Smallpox and vaccinia viruses belong to the family, Poxviridae.
Viral vectors from different vaccinia strains have been derived from the original smallpox vaccine and are used to obtain high expression levels of foreign genes.  Attenuated and replication defective vaccinia strains (NYVAC) have been developed for use as viral vectors, as well as avipoxviruses (ALVAC, TROVAC), suipox and sheeppox/goatpox.

Potential Health Hazards

Vaccinia can cause severe disease in people with active skin disorders (eczema, psoriasis), pregnant women, and in immune-compromised individuals.  

Modes of Transmission

Infection can occur through ingestion, parenteral inoculation, and droplet or aerosol exposure to mucous membranes or broken skin.  Some poxviruses can be transmitted by fomites (inanimate objects).

Vaccinia is spread through close personal contact.  Shedding of virus begins with the appearance of a papule, reaches a maximum 4 to 14 days after inoculation, and can persist until the lesion scabs over.

Laboratory Acquired Infections

Laboratory-associated infections with poxiviruses, including smallpox, vaccinia, yaba and tanapox, have previously been reported.  A recent report described a case of ocular vaccinia infection in an unvaccinated laboratory worker.

Host Range

Vaccinia virus has a very broad host range; the virus can replicate in vitro and in vivo in birds and humans.  The virus does not occur naturally in humans and has no animal reservoir; vaccinia is now considered a laboratory virus.
Avipoxviruses are restricted to growth (replication) in avian species; however, these viruses can infect mammalian cells.


Poxviruses are able to survive for a considerable period of time in dried material (including detached vaccination scabs) and when dried onto inanimate surfaces.
Lyophilized vaccinia virus maintains potency for 18 months at 4° C.

Laboratory Practices

Biosafety level 2 practices and facilities must be used for activities involving poxviruses/viral vectors that pose an infection hazard.

  •  Biohazard signs and labels must be displayed in areas and on equipment where vaccinia is used and stored.  This includes, but is not limited to, laboratory entrance doors, biological safety cabinets, incubators, refrigerators, and freezers.
  • Use a biological safety cabinet (BSC) (a.k.a. tissue culture hood) for manipulations that can generate aerosols, such as pipetting, harvesting, infecting cells, filling tubes/containers, and opening sealed centrifuge canisters.  If a procedure cannot be done in a BSC and only on an open bench, use a plastic shield to prevent exposure through inhalation or splashing.
  • Use aerosol containment devices when centrifuging.  These include sealed canisters that fit in the centrifuge bucket, covers for the centrifuge bucket, heat sealed tubes, or sealed centrifuge rotors.  Rotors should be removed and opened inside a BSC.  Centrifuge tubes should be filled and opened in a BSC.
  • Vacuum lines must be protected with liquid disinfectant traps and micron filters.

In addition, Biosafety level 2 practices and facilities must be used for activities involving highly attenuated recombinant vaccinia strains, including MVA and NYVAC, and for recombinant avipoxviruses, including ALVAC and TROVAC.  While these vectors are unable to produce infectious virus in humans, the use of viral-based vectors for gene delivery to mammalian cells has been assigned BSL2 containment by the Institutional Biosafety Committee (IBC) unless justification for a lower classification is proposed by the PI and approved by the IBC.

Personal Protective Equipment

Personal protective equipment (PPE) includes, but is not limited to:

  •  Disposable gloves (nitrile, latex, etc.).
  •  Lab coat when working in the area.  Remove when leaving the laboratory.
  •  Goggles for splash protection.

Precautions When Using Animals

Animal use requests are made to the Institutional Animal Care and Use Committee (IACUC) by submitting an Animal Care and Use Form (ACURF).

When animals are infected with vaccinia virus, the Animal Biosafety Level of the project will be generally assigned to ABSL-2a
Cases have been documented in which transmission of vaccinia virus was observed from a recently vaccinated human to wild and domesticated mammals.  Conversely, infected animals are also a potential source of infection to exposed unvaccinated laboratory staff.

When animals are infected with poxvirus/vectors other than vaccinia (ALVAC, NYVAC, MVA), the Animal Biosafety Level of the project will be generally assigned to ABSL-1.  
Animal cages must be labeled with a biohazard sign.

Recombinant Poxviral Research

Protocols involving recombinant poxviral vectors must be approved by the Institutional Biosafety Committee (IBC); complete an online "rDNA Registration Document”.

Employee Exposure

Eye Exposure – Rinse eyes in an eyewash for at least 15 minutes.
Skin Exposure – Rinse skin with soap and water.
Accidental Needlestick Injury – Scrub contaminated skin with soap and water.

Report Incidents and Seek Treatment – Report actual or suspected exposure incidents to your supervisor immediately.  Seek treatment at the Worker’s Health Clinic, if necessary.  The clinic is located on the first floor of Boyd Tower – General Hospital, phone number 356-3631.  If the incident occurs after 4:30pm, during the weekend, or on a holiday, proceed to UIHC’s Emergency Treatment Center (ETC),  phone number 356-2233.

  • Incubation Period – from 5 to 10 days.•
  • Symptoms – include rash, vesicular or pustular lesion, generalized vaccinia with multiple lesions.  Major complications include encephalitis, progressive vaccinia or eczema vaccinatum.
  • Vaccinia Immunization – (smallpox vaccine) is recommended for laboratory staff working directly with vaccinia and vaccinia virus recombinants.  Vaccination can have side effects that range from mild fever and fatigue to rare, severe and at times fatal events including generalized vaccinia, eczema vaccinatum, and fetal infection; therefore, contraindications should be studied and carefully followed.

    University staff working with vaccinia are offered the vaccine, at no cost to the employee, and must sign a form acknowledging that they understand the risk of acquiring infection from occupational exposure and either accepting or declining the vaccination at this time. Forms are returned to Biological Safety Staff at EHS, 100 EHS; vaccination is provided through the University Employee Health Clinic (UEHC).

    Information and contraindications are available on CDC’s website and can be discussed with physicians at EHC. 
  • Prophylaxis – none; however, vaccinia immune globulin and methisazone may be used to treat complications.

Spill and Disposal Procedures

For spills outside a biological safety cabinet, leave the area while holding your breath.  Once outside the area, wash hands and face with soap and water.  Do not allow anyone inside the area or room where the spill occurred.  Allow 30 minutes for the aerosols to settle.  Enter the room wearing required protective clothing, gently cover the spill with paper towels, and apply disinfectant starting at the perimeter and working towards the center.  Allow the disinfectant to remain on the spill for at least 30 minutes before initiating spill clean up.  After initial clean up, disinfect the area a second time.

For spills inside a biological safety cabinet, cover the spill with paper towels or wipes.  Gently pour disinfectant over the spill area.  Let the disinfectant soak for 30 minutes before cleaning up the spill.  After initial clean up, disinfect the area a second time.

Contaminated materials must be disposed of as biohazardous waste.

Decontaminate adjacent surfaces with a bleach solution.


Disinfectants should be allowed a minimum of 20-30 minutes contact time.  Use one of the following:

  • Sodium hypochlorite (1-10% dilution of fresh bleach).
  • 2% glutaraldehyde, formaldehyde.


Autoclave cultures for 30 minutes at 121° C or 250° F (15lbs per square inch of steam pressure).
Disinfect work surfaces using an effective germicide (see above).  This may be followed by an alcohol wipe to lessen the corrosive nature of the germicide.

Transport Requirements

Materials must be appropriately contained and labeled for transport within the University.  Shipping infectious substances, diagnostic specimens, and/or shipping with dry ice off-campus require training and certification.  See EHS’s fact sheet “Transporting and Shipping Infectious Substances”.

If You Have Questions

Contact EHS’s Biological Safety Section at 5-8501.

Information and References

  • Debyser, Z. 2003. A short course on virology / vectorology / gene therapy. Current Gene Therapy. 3:495-9.
  • Health Canada Office of Laboratory Security. May, 2001.  Infectious Substances MSDS Web Site.  Vaccinia virus. Retrieved May 2009.
  • Health and Safety Executive, United Kingdom. 2000. Advisory Committee on Genetic Modification. Guidance on commonly used vectors. Part 2B-Annex III.
  • Lewis, F.M.T., et. al. 2006. Infection in laboratory worker, Philadelphia, 2004. Emerging Infectious Diseases. 12:134-7.
  • Vanderplasschen, A. and P.-P. Pastoret. 2003. The uses of poxviruses as vectors. Current Gene Therapy. 3:583-95.
  • U.S. Department of Health and Human Services Centers for Disease control and Prevention and National Institutes of Health. (2007 February)  Biosafety in Microbiological and Biomedical Laboratories (BMBL) 5th Edition.  Retrieved May 2009.  Updated 02/2015