Varicella vaccine given subcutaneously (under the skin). It is recommended for all children under 13 and for everyone 13 or older who has never had chickenpox. In the United States two doses are recommended. In the first case a first dose is administered at 12 to 15 months and a second dose at age 4–6 years. For people older than 13 the two doses are administered 4 to 8 weeks apart. The varicella vaccine did not become widely available in the United States until 1995. In the UK, the vaccine is only recommended in people who are particularly vulnerable to chickenpox. The
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