Modified vaccinia Ankara
attenuated vaccine of a poxvirus
Modified vaccinia Ankara (MVA) is an attenuated (weakened) strain of the vaccinia virus. It is being used as a vaccine (called MVA-BN, brand names: Imvanex in the EU, Imvamune in Canada, and Jynneos in the US) against smallpox and mpox, having fewer side effects than smallpox vaccines derived from other poxviruses.
This third-generation smallpox vaccine has the advantage that it cannot reproduce complete virions in human cells, "the block of the MVA life cycle occurs at the step of virion assembly resulting in assembly of immature virus particles that are not released from the infected cell."
By inserting antigen genes into its genome, modified vaccinia Ankara virus is also used as an experimental viral vector for vaccines against non-poxvirus diseases.
Development as a poxvirus vaccine
The traditional smallpox vaccine, which was used in the smallpox eradication campaign 1958–1977, consists of a live vaccinia virus which can replicate in humans but usually does not cause disease. It can however sometimes lead to serious side effects. Modified vaccinia Ankara virus is a highly attenuated strain of vaccinia virus that was developed in Munich, Germany between 1953 and 1968. It was produced by more than 500 serial passages of vaccinia virus (from a wild strain discovered by the Turkish vaccine institute of Ankara called the chorioallantois vaccinia Ankara) in chicken embryo fibroblasts. After testing the safety and effectiveness as a vaccine, it was approved in Germany in 1977, and then given to about 120,000 people until 1980, when smallpox vaccinations ended in Germany. No severe adverse events were seen during this time.
It was later found that through the passaging, modified vaccinia virus Ankara had lost about 10% of the ancestral vaccinia genome and with it the ability to replicate efficiently in most mammalian cells.
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