On 8 February 2011, the Ministry of Health in Sierra Leone notified WHO of two cases of yellow fever in Jahun village in Bonthe district, Southern province.
Sierra Leone benefited from a yellow fever preventive mass vaccination campaign in 2009, which covered 11 out of 13 districts in the country, excluding Bonthe and Bombali districts.
On 5 March 2011, the Ministry of Health of Sierra Leone began a response vaccination campaign targeting 144,479 people aged nine months and above, excluding pregnant women in Bonthe district.