Live virus reference strain
Live virus reference strain (LVRS) refers to a common strain of a virus that is selected for the manufacture of a preventative vaccine. It is most commonly used in reference to the seasonal Influenza vaccines developed by the Centers for Disease Control every year. However, it can also refer to other virus strains. 
Annual Influenza vaccine development
Each year, with the assistance of the World Health Organization, the Centers for Disease Control in Atlanta, Georgia, select strains of Influenza virus that are most likely to provide effective immunization to a broad spectrum of individuals.
Vaccine viruses are chosen to maximize the likelihood that the vaccine will protect against the viruses most likely to spread and cause illness among people during the upcoming flu season. WHO recommends specific vaccine viruses for influenza vaccine production, but then individual countries make their own decisions for licensing of vaccines in their country. In the United States, the Food and Drug Administration determines what viruses will be used in U.S.-licensed vaccines.
- "CDC - Seasonal Influenza (Flu) - Selecting the Viruses in the Influenza (Flu) Vaccine". Cdc.gov. Retrieved 2013-09-24.
- "CDC - Seasonal Influenza (Flu) - Vaccine Virus Selection for the 2012-2013 Influenza Season". Cdc.gov. Retrieved 2013-09-24.
- Declan Butler. Vaccine decisions loom for new flu strain. 12 May 2009 Nature. 12 May 2009. News. doi:10.1038/459144a