Nigeria: Lassa Fever Outbreak - Jan 2023

From week 1 through week 3, 2023, a total of 244 new confirmed cases of Lassa fever, including 37 deaths with a case fatality ratio of 15.2%, have been reported in 16 states. The highest number of cases was reported in Ondo (90) and Edo (89) states, followed by Bauchi (13), Taraba (10), Benue (9), Ebonyi (9), Nasarawa (7), Plateau (5), Kogi (4), Anambra (2), Delta (1), Oyo (1), Adamawa (1), Enugu (1), and Imo (1) states; one case was reported from the Federal Capital Territory (FCT) (1). About 79% of all confirmed Lassa fever cases were reported from three states (Ondo, Edo, and Bauchi), while 21% were reported from 13 states. Of the 79% of confirmed cases, Ondo reported 37%, Edo 36%, and Bauchi 5%. In total for 2023, 16 States have recorded at least one confirmed case across 50 Local Government Areas. Of the reported cases, the predominant age group affected is 21-30 years (range: 1 to 79 years) and the Median age is 30 years. The male-to-female ratio for confirmed cases is 1:0.9. Five confirmed cases and one death were reported among health workers. In week 3 alone, the number of new confirmed cases increased from 77 in week 2, 2023 to 137 cases and the number of deaths from six in week 2 to 18 in week 3. These cases were reported from Ondo, Edo, Taraba, Benue, Nasarawa, Bauchi, Ebonyi, Plateau, Kogi, Anambra, Delta, FCT, Adamawa, and Enugu states. A total of two confirmed cases among health Care workers were reported in the reporting week. Compared to the previous year 2022, from week 1 to week 3, the number of confirmed cases has increased from 170 cases in 2022 to 244 cases in 2023. A total of 12 states and 37 Local Government Areas (LGAs) were affected in 2022 against 16 states and 50 LGAs in 2023. However, the case fatality ratio was higher in 2022 (18.8%, 32/170) compared to 2023 (15.1%, 37/244) for the same period. (WHO, 8 Feb 2023)

Nigeria is currently experiencing a large outbreak of Lassa fever, with 4702 suspected cases, five probable cases, and 877 confirmed cases between epidemiological weeks 1 and 15 of 2023 (week ending 16 April). Among confirmed cases, there have been 152 deaths (CFR 17%). Lassa fever is endemic in Nigeria and parts of West Africa where the multimammate rat, the main reservoir of the Lassa virus, is common. Responding to the current outbreak is challenging due to the need to respond to multiple emergencies simultaneously. (WHO, 1 May 2023)

Cumulatively from week 1 to week 20, 2023, 162 deaths have been reported with a case fatality rate (CFR) of 17.2% which is lower than the CFR for the same period in 2022 (19.8%). In total for 2023, 28 States have recorded at least one confirmed case across 106 Local Government Areas. (Gov't of Nigeria, 21 May 2023)

In week 23, the number of new confirmed decreased from 7 in epi week 22, 2023 to 1 case. This was reported from Edo State. Cumulatively from week 1 to week 23, 2023, 164 deaths have been reported with a case fatality rate (CFR) of 17.1% which is lower than the CFR for the same period in 2022 (20.0%). In total for 2023, 28 States have recorded at least one confirmed case across 106 Local Government Areas. (Gov't of Nigeria, 11 Jun 2023)

In week 29, 2023, Nigeria recorded 114 cases of Lassa fever, with zero deaths. From week 1 to week 29, a cumulative total of 6597 suspected cases were reported across 28 states and 111 local government areas. Among these cases, 1009 were confirmed, and 171 are deaths (CFR 16.9 %). The states of Ondo, Edo, and Bauchi account for 73% of all confirmed cases. The age group most affected is 21-30 years, ranging from 1 to 93 years. Furthermore, the number of suspected cases has shown an increase compared to the corresponding period in 2022. (WHO, 30 Jul 2023)

Cumulatively from week 1 to week 41, 2023, 188 deaths have been reported with a case fatality rate (CFR) of 17.2% which is lower than the CFR for the same period in 2022 (18.9%). (Gov't of Nigeria, 15 Oct 2023)

In week 37, 2023, Nigeria recorded 79 cases of Lassa fever, with zero deaths. From week 1 to week 37, a cumulative total of 7 352 suspected cases were reported across 28 states and 112 local government areas. Among these cases, 1 068 were confirmed, and 181 are deaths (CFR 16.9%). The states of Ondo, Edo, and Bauchi account for 75% of all confirmed cases. (WHO, 9 Nov 2023)

In week 51, the number of new confirmed cases increased from 10 in epi week 50, 2023 to 26 cases. These were reported in Bauchi, Ondo, Taraba, and Plateau States. Cumulatively from week 1 to week 51, 2023, 215 deaths have been reported with a case fatality rate (CFR) of 17.5% which is lower than the CFR for the same period in 2022 (17.9%). In total for 2023, 28 States have recorded at least one confirmed case across 121 Local Government Areas. (Gov't of Nigeria, 24 Dec 2023)

As of week 21, of 2024, 6464 suspected cases, including 897 laboratory-confirmed cases, were reported, with 162 reported deaths among confirmed cases, resulting in a CFR of 18.1 %. Confirmed cases were reported from 28 states and 125 LGAs. three out of 36 states (Edo, Ondo, and Bauchi) account for 65% of confirmed cases. (WHO, 16 Jun 2024)