Dexamethasone is a corticosteroid which can modulate inflammatory-mediated tissue damage associated with a wide range of infectious diseases. Dexamethasone is routinely used for treatment of tuberculous meningitis and for pneumococcal meningitis in adults. In Coronavirus Disease 2019 (COVID-19) dexamethasone is also effectively preventing immune mediated damage of the lungs. There is also indication that dexamethasone may be promising in severe LF.

Lassa fever (LF) is a severe and often fatal systemic disease in humans. It is caused by the Lassa virus (LASV). Vaccines are not available yet and treatment options are limited to supportive care and ribavirin. Recent LF outbreaks in Nigeria showed an exceptionally high and increasing incidence of LF cases LF affects a large number of countries in West Africa. The pathophysiology of LF is not fully understood yet. It is hypothesized that the damage mediated by the host's defence is plays a key role in the pathophysiology of severe LF. Dexamethasone is considered to dampen the overactive immune response in a range of infectious diseases and thus preventing consecutive damage mediated by the host's immune system, while the antiinfective therapy is effectively treating the underlying pathogen. At the Irrua Specialist Teaching Hospital (ISTH) in Nigeria, one of the largest treatment centres for LF in West-Africa, dexamethasone has been successfully used in clinical practice to manage co-infections of LASV and Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2).

To evaluate Dexamethasone for the treatment of moderate to severe LF cases, a prospective open label randomized controlled phase II clinical trial will be conducted:

1. Standard of care antiviral ribavirin therapy
2. Standard of care antiviral ribavirin therapy + dexamethasone

The primary objective is to assess safety and tolerability of dexamethasone in moderate to severe LF when administered as adjunct treatment. Secondary objectives are to assess the effect of the study intervention on disease progression; to assess immunological and virological impact of dexamethasone therapy and the characterization of population pharmacokinetic characteristics for patients treated with adjunct dexamethasone therapy.

Inclusion Criteria:

• Age ≥ 18 years
• LF confirmed by RT-PCR (reverse-transcription polymerase chain reaction) with a cycle threshold (Ct) value < 30
• Signs of significant health impairment as evidenced by any of the following:
• Alert, confusion, voice, pain, unresponsive (ACVPU) other than A
• Systolic blood pressure < 90 mmHg
• Seizure(s), meningism, coma, focal neurological deficit
• AST (GOT) >3xULN
• ALT (GPT) > 3xULN
• KDIGO 2 or more severe based on serum creatinine only
• Active macroscopic bleeding
• O2 saturation < 92

Exclusion Criteria:

• Pregnancy (evidenced by positive urine pregnancy test in women of child-bearing potential)
• Lactation following live birth
• Known intolerance and contra-indications to ribavirin or dexamethasone
• Patients who already received a corticosteroid within the preceding 7 days
• Investigator's valuation that patient might be put to substantial risk by participating in this trial
• Patients receiving end-of-life care as judged by the investigator

Case by case decision upon request