Vaccinia

Vaccinia

Electron micrograph of the Vaccinia virus

Vaccinia is a virus belonging to the Poxviridae family, which is used as a live virus vaccine for the prevention of smallpox. It is a member of the Orthopoxvirus genus, which also includes the variola virus (the causative agent of smallpox), the cowpox virus, and the monkeypox virus. Vaccinia virus is notable for its role in the successful eradication of smallpox, a major achievement in public health.

Structure and Genetics

Vaccinia virus is a large, complex, enveloped virus with a linear double-stranded DNA genome. The genome is approximately 190 kilobase pairs in length and encodes for around 200 proteins. The virus has a complex structure with a biconcave core and lateral bodies, which are thought to contain enzymes essential for the early stages of infection.

Life Cycle

The life cycle of the vaccinia virus begins with attachment to the host cell surface, followed by entry into the cell. Once inside, the virus uncoats and releases its DNA into the cytoplasm. Unlike many other DNA viruses, vaccinia replicates entirely in the cytoplasm of the host cell. The virus uses its own machinery to transcribe and replicate its DNA, producing viral proteins and assembling new virions. These new virions are then released from the host cell to infect other cells.

Use in Vaccination

A smallpox vaccination site on the arm

Vaccinia virus is used in the smallpox vaccine, which was the first successful vaccine to be developed. The vaccine is administered by scarification, a method that involves pricking the skin with a bifurcated needle that has been dipped in the vaccine solution. This method creates a localized infection that induces immunity to smallpox.

The use of vaccinia virus in vaccination led to the global eradication of smallpox, declared by the World Health Organization in 1980. The vaccine is still used today for certain high-risk groups, such as laboratory workers who handle orthopoxviruses and military personnel.

Safety and Side Effects

While the smallpox vaccine is generally safe, it can cause side effects, particularly in individuals with weakened immune systems or certain skin conditions. Common side effects include fever, fatigue, and a localized rash at the site of vaccination. More serious complications, such as eczema vaccinatum, progressive vaccinia, and postvaccinal encephalitis, are rare but can occur.

Research and Applications

Vaccinia virus is also used as a tool in biotechnology and genetic engineering. Its ability to accommodate large foreign DNA sequences makes it an attractive vector for vaccine development against other infectious diseases and for cancer immunotherapy. Researchers are exploring its use in developing vaccines for diseases such as HIV/AIDS, influenza, and cancer.

Related Pages

• Smallpox
• Poxviridae
• Orthopoxvirus
• Variola virus
• Cowpox
• Monkeypox