Stanford University

Pox Viruses/Vaccinia Fact Sheet

The poxviruses are the largest known DNA viruses and are distinguished from other viruses by their ability to replicate entirely in the cytoplasm of infected cells. Poxviruses do not require nuclear factors for replication and, thus, can replicate with little hindrance in enucleated cells. The core contains a 200-kilobase (kb), double-stranded DNA genome and is surrounded by a lipoprotein core membrane.

Recombinant Vaccinia vectors: Vaccinia virus can accept as much as 25 kb of foreign DNA, making it useful for expressing large eukaryotic and prokaryotic genes. Foreign genes are integrated stably into the viral genome, resulting in efficient replication and expression of biologically active molecules. Furthermore, posttranslational modifications (e.g., methylation, glycosylation) occur normally in the infected cells.

Vaccinia is used to generate live recombinant vaccines for the treatment of other illnesses. Modified versions of vaccinia virus have been developed for use as recombinant vaccines. The modified Ankara strain (MVA) of vaccinia virus was developed by repeated passage in a line of chick embryo fibroblasts. NYVAC is another attenuated form of the vaccinia virus that has been used in the construction of live vaccines. NYVAC has a deletion of 18 vaccinia virus genes that render it less pathogenic.

What are the hazards?

Virus disease of skin induced by inoculation for the prevention of smallpox – vesicular or pustular lesion, area of induration or erythema surrounding a scab or ulcer at inoculation site; major complications encephalitis, progressive vaccinia (immunocompromised susceptible), eczema vaccinatum, fetal vaccinia; minor complications – generalized vaccinia with multiple lesions; auto-inoculation of mucous membranes or abraded skin, benign rash, secondary infections; complications are serious for those with eczema or who are immunocompromised.


Communicable to unvaccinated contacts via contact with mucosal membranes or cuts in skin.

Laboratory Hazards

Ingestion, parenteral injection, droplet or aerosol exposure of mucous membranes or broken skin with infectious fluids or tissues.

Laboratory hazards ppe
Exposure of mucus membrane (eyes, nose, mouth) Use of safety goggles or full face shields. Use of appropriate face mask
Injection Use of safety needles; NEVER re-cap needle or remove needle from syringe
Aerosol inhalation Use of appropriate respiratory protection
Direct contact with skin Gloves, lab coat, closed shoes

The above PPE are often required IN ADDITION to working in a certified Biosafety Cabinet.

Susceptibility to disinfectants: Susceptible to 1% sodium hypochlorite, 2% glutaraldehyde, formaldehyde

Use in Lab: BSL-2

Use with Animals: ABSL-2 housing.

How can I protect myself?

Consultation is available to determine if vaccination with the Smallpox vaccine is appropriate for personnel using vaccinia.


Vaccinia immune globulin and an antiviral medication may be of value in treating complications.

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