Last reviewed: 23 May 2021
Last updated: 06 Apr 2021
03 Feb 2021

Baloxavir marboxil approved for post-exposure prophylaxis of influenza

The approved indication for baloxavir marboxil has been expanded in the US and in Europe to include post-exposure prophylaxis of influenza for patients 12 years of age and older.

The safety and efficacy of baloxavir marboxil in post-exposure prophylaxis is supported by one multi-centre, double-blind, randomised, placebo-controlled trial conducted in Japan during the 2018-2019 season.

  • Participants were assigned in a 1:1 ratio to receive either a single dose of baloxavir marboxil or placebo. The primary end point of the trial was clinical influenza, confirmed by reverse transcriptase-polymerase chain reaction testing over a period of 10 days.

  • The study found that the percentage of participants in whom clinical influenza developed was significantly lower in the baloxavir marboxil group than in the placebo group (1.9% vs. 13.6%) (adjusted risk ratio 0.14; 95% confidence interval [CI] 0.06 to 0.30; P<0.001). The incidence of adverse events reported during the trial was similar in the two groups (22.2% in the baloxavir marboxil group and 20.5% in the placebo group).

Baloxavir marboxil was previously approved for the treatment of uncomplicated influenza in patients 12 years of age and older who have been symptomatic for no more than 48 hours.

See Management: approach

See Management: treatment algorithm

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History and exam

Key diagnostic factors

  • winter season
  • current influenza outbreak
  • unvaccinated
  • fever with cough

Other diagnostic factors

  • sore throat
  • cervical lymphadenopathy
  • dyspnoea

Risk factors

  • age ≥65 years
  • age 6-59 months
  • chronic cardiovascular or respiratory conditions
  • diabetes
  • haemoglobinopathy
  • immunocompromise
  • chronic kidney disease (CKD)
  • pregnancy
  • carers and household contacts of high-risk groups
  • healthcare workers

Diagnostic investigations

Investigations to consider

  • viral culture
  • direct immunofluorescent antibody staining
  • reverse transcriptase-polymerase chain reaction
  • serology
  • enzyme immunoassay (EIA)
  • rapid diagnostic tests
  • chest x-ray

Treatment algorithm


Staff Physician

Department of Pulmonary, Allergy and Critical Care

Cleveland Clinic




CR declares that she is on Advisory boards for CSL Behring and Speakers Bureau Biocryst.

Peer reviewersVIEW ALL

Associate Professor

Medical Director of Infection Control

Infectious Disease

Department of Medicine

SUNY Upstate Medical University




WJ declares that he has no competing interests.

Associate Professor of Clinical Medicine and Environmental Health Sciences

Columbia University College of Physicians and Surgeons

New York



RLM declares that she has no competing interests.


SUNY Buffalo School of Medicine

Division Allergy and Immunology




MS declares that he has no competing interests.

Associate Professor

Department of General Practice and Primary Health Care

Ghent University




ADS declares that she has no competing interests.

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