The vaccine is supplied in separate vials, one containing the adjuvant, and the other the inactivated virus,[11] which require mixing before intramuscular injection. Originally it was thought that two doses given 21 days apart would be required for full efficacy.[citation needed] Subsequent testing has allowed the UK programme to consist of just a single dose for most people, with a two-dose schedule for children under the age of 10 years and immunocompromised adults.[12]