Immunological insights into COVID-19 in Southern Nigeria

Introduction

One of the unexpected outcomes of the COVID-19 pandemic was the relatively low levels of morbidity and mortality in Africa compared to the rest of the world. Nigeria, Africa's most populous nation, accounted for less than 0.01% of the global COVID-19 fatalities. The factors responsible for Nigeria's relatively low loss of life due to COVID-19 are unknown. Also, the correlates of protective immunity to SARS-CoV-2 and the impact of pre-existing immunity on the outcome of the COVID-19 pandemic in Africa are yet to be elucidated. Here, we evaluated the natural and vaccine-induced immune responses from vaccinated, non-vaccinated and convalescent individuals in Southern Nigeria throughout the three waves of the COVID-19 pandemic in Nigeria. We also examined the pre-existing immune responses to SARS-CoV-2 from samples collected prior to the COVID-19 pandemic.

Methods

We used spike RBD and N- IgG antibody ELISA to measure binding antibody responses, SARS-CoV-2 pseudotype assay protocol expressing the spike protein of different variants (D614G, Delta, Beta, Omicron BA1) to measure neutralizing antibody responses and nucleoprotein (N) and spike (S1, S2) direct ex vivo interferon gamma (IFNγ) T cell ELISpot to measure T cell responses.

Result

Our study demonstrated a similar magnitude of both binding (N-IgG (74% and 62%), S-RBD IgG (70% and 53%) and neutralizing (D614G (49% and 29%), Delta (56% and 47%), Beta (48% and 24%), Omicron BA1 (41% and 21%)) antibody responses from symptomatic and asymptomatic survivors in Nigeria. A similar magnitude was also seen among vaccinated participants. Interestingly, we revealed the presence of preexisting binding antibodies (N-IgG (60%) and S-RBD IgG (44%)) but no neutralizing antibodies from samples collected prior to the pandemic.

Discussion

These findings revealed that both vaccinated, non-vaccinated and convalescent individuals in Southern Nigeria make similar magnitude of both binding and cross-reactive neutralizing antibody responses. It supported the presence of preexisting binding antibody responses among some Nigerians prior to the COVID-19 pandemic. Lastly, hybrid immunity and heterologous vaccine boosting induced the strongest binding and broadly neutralizing antibody responses compared to vaccine or infection-acquired immunity alone.

Epidemiologic and Clinical Features of Lassa Fever Outbreak in Nigeria, January 1-May 6, 2018

The outbreak, which resulted in 423 confirmed cases and 106 deaths, was the largest recorded Lassa fever outbreak.

Lassa fever (LF) is endemic to Nigeria, where the disease causes substantial rates of illness and death. In this article, we report an analysis of the epidemiologic and clinical aspects of the LF outbreak that occurred in Nigeria during January 1–May 6, 2018. A total of 1,893 cases were reported; 423 were laboratory-confirmed cases, among which 106 deaths were recorded (case-fatality rate 25.1%). Among all confirmed cases, 37 occurred in healthcare workers. The secondary attack rate among 5,001 contacts was 0.56%. Most (80.6%) confirmed cases were reported from 3 states (Edo, Ondo, and Ebonyi). Fatal outcomes were significantly associated with being elderly; no administration of ribavirin; and the presence of a cough, hemorrhaging, and unconsciousness. The findings in this study should lead to further LF research and provide guidance to those preparing to respond to future outbreaks.

Increase in Lassa Fever Cases in Nigeria, January-March 2018

We reviewed data pertaining to the massive wave of Lassa fever cases that occurred in Nigeria in 2018. No new virus strains were detected, but in 2018, the outbreak response was intensified, additional diagnostic support was available, and surveillance sensitivity increased. These factors probably contributed to the high case count.

A cluster of nosocomial Lassa fever cases in a tertiary health facility in Nigeria: Description and lessons learned, 2018

BACKGROUND

Lassa fever is an acute viral haemorrhagic disease endemic in Nigeria. The 2018 Lassa fever outbreak in Nigeria was unprecedented, with 8% of all cases occurring among healthcare workers (HCWs). A disproportionately high number of these infections occurred in HCWs working in a tertiary health facility in Nigeria. This paper describes the cluster of Lassa fever infections among HCWs in a treatment centre and the lessons learnt.

METHODS

We analysed clinical, epidemiological and laboratory data from surveillance and laboratory records kept during the 2018 outbreak. Interviews were conducted with surviving HCWs using a questionnaire developed specifically for the investigation of Lassa fever infections in HCWs. Descriptive analysis of the data was performed in Microsoft excel.

RESULTS

The index case was a 15-year-old male who presented at the health facility with fever and uncontrolled nasopharyngeal bleeding, following a recent uvulectomy by a traditional healer. Overall, 16 HCWs were affected (15 confirmed and 1 probable) with five deaths (CFR-31.6%). Of the 15 confirmed cases, five (33.3%) were asymptomatic. Nine HCWs were direct contacts of the index case; the remaining six HCWs had no direct contact with the index case. HCW interviews identified a low index of suspicion for Lassa fever leading to inadequate infection prevention and control (IPC) practices as possible contributing factors to nosocomial transmission.

CONCLUSION

Maintaining a high index of suspicion for Lassa fever in all patients, especially in endemic areas, is essential in adhering to adequate IPC practices in health facilities in order to prevent nosocomial transmission of Lassa fever among HCWs. There is a need to continually train and sensitise HCWs on strict adherence to IPC measures while providing care, irrespective of a patient's provisional diagnosis.