Antibody levels at month 3 (one month post-dose number two) are substantially higher than at month 24 (18 months post-dose number three), suggesting that protection is achieved by month 3 and perhaps earlier. In 2014, the World Health Organization (WHO) recommended that countries offer the vaccine in a two dose schedule to girls aged under 15, with each dose at least six months apart. The United Kingdom, Switzerland, Mexico, and Quebec province of Canada are among the countries or territories that have implemented this . The CDC recommended the vaccines be delivered in two shots over six months.