MMRV vaccine mumps, rubella (German measles), and varicella (chickenpox) because the risks of these diseases far outweigh the risks of vaccinating against them. In particular, the World Health Organization recommends varicella vaccination in countries where the vaccine is affordable, the disease is a relatively important problem, and high and sustained vaccine coverage can be achieved. The U.S. and a few other countries have widely implemented this. MMR and varicella vaccine are given at roughly the same time and a booster injection is recommended for both. The MMRV vaccine, a combined MMR and varicella vaccine, simplifies administration of the vaccines. Doctors are advised
Rare disease treated, are excluded from their definition. The definitions used in the medical literature and by national health plans are similarly divided, with definitions ranging from 1/1,000 to 1/200,000. Because of definitions that include reference to treatment availability, a lack of resources, and severity of the disease, the term "orphan disease" is used as a synonym for "rare disease". But in the United States and the European Union, "orphan diseases" have a distinct legal meaning. The United States' Orphan Drug Act includes both rare diseases and any non-rare diseases "for which there is no reasonable expectation that the cost of developing