ArkBio RSV Antiviral Drug Ziresovir Receives FDA Approval for Phase II Clinical Trial

The US FDA cleared ArkBio to start a Phase II clinical trial for ziresovir, a direct-acting antiviral drug targeting severe respiratory syncytial virus (RSV) infections.

Shanghai Ark Biopharmaceutical Co., Ltd. announced that the U.S. Food and Drug Administration (FDA) has approved ziresovir (AK0529) for a phase II clinical trial in severely ill RSV-infected infant patients, involving those in the pediatric intensive care unit (PICU).

Serious RSV Infection: An Imperative Unmet Requirement in PICU

RSV is an important pathogen of lower respiratory tract infections (LRTIs) in infants and young children worldwide, which leads to around 33 million LRTI cases, 3.6 million hospitalizations, and more than 100,000 deaths yearly. Severely ill RSV-infected infants often need admission to the PICU for intensive care, such as respiratory support, with increasing disease progression, significant challenges, and a significant healthcare burden. There is currently no approved RSV-driven antiviral therapy worldwide; healthcare management remains restricted to symptomatic and supportive care, such as oxygenation, leaving an urgent unmet need for efficient antiviral treatment in hospitalized RSV-infected patients with serious disease.

Ziresovir Advances to Treat Severely Infected Infant Patients

Ziresovir is the first direct RSV antiviral therapeutic to complete a phase III clinical trial with positive results. The clinical research in 1- to 24-month-old patients conducted in China demonstrated that ziresovir potentially lowers viral load, speeds up the resolution of respiratory symptoms, and predominantly lowers the challenges of recurrent wheezing and asthma over a 24-month follow-up period, with a promising safety profile. Important findings from the clinical output have been published in The New England Journal of Medicine and The Lancet Child & Adolescent Health. In 2025, ziresovir was included as the only therapeutic drug in the WHO's Paediatric Drug Optimization for Respiratory Syncytial Virus publication. The newly approved phase II clinical trial signifies the extension of ziresovir's clinical advancement into the most severely ill RSV patients, showing a significant milestone in the healthcare development of ziresovir worldwide.

FDA-Approved Phase II Clinical Trial

The permitted multicenter, randomized, double-blind, placebo-controlled phase II clinical trial predominantly focuses on severely ill RSV-infected infants needing hospitalization in the PICU, one of the most significant RSV patient populations with the most urgent clinical management requirements. This clinical trial is intended to evaluate the healthcare effectiveness of ziresovir, particularly the length of oxygen treatment and continued recovery time, offering the clinical basis for future registrational trials.

According to Towards Healthcare, the antiviral drugs market is projected to grow significantly, with estimates indicating the market size will increase from USD 65.13 billion in 2026 to approximately USD 89.86 billion by 2035, expanding at a CAGR of 3.64% from 2026 to 2035. Antiviral drugs are a class of medicines specifically applied for the management of viral infections. Drugs that combat viral infections are called antiviral therapeutics. Viruses are significant pathogenic agents that cause several serious diseases in humans, animals, and plants. Viruses cause major diseases in humans, from self-resolving diseases to acute and chronic diseases. Antiviral drugs that directly target viruses include inhibitors of virus attachment, inhibitors of virus entry, uncoating inhibitors, polymerase inhibitors, protease inhibitors, inhibitors of nucleoside and nucleotide reverse transcriptase, and inhibitors of integrase.

About ArkBio

ArkBio is a commercial-stage healthcare organization focused on the discovery and advancement of innovative medicine for respiratory and pediatric diseases. Founded in 2014, the organization has established proprietary technology platforms and a differentiated R&D pipeline via internal innovation and strategic partnerships. Significant pipeline assets include: ziresovir (AK0529), the first direct-acting antiviral for RSV with positive phase 3 results; AK3280, a best-in-class anti-fibrotic agent with positive phase 2 results in idiopathic pulmonary fibrosis, presently in phase 3 registrational trials; AK0901, approved and commercialized in China for ADHD treatment. The organization also has multiple first-in-class or best-in-class innovative drug candidates in healthcare or preclinical advancement. ArkBio has established strategic collaborations with multinational pharmaceutical organizations involving Roche and Genentech, leading academic institutions including The Scripps Research Institute and the Institute of Microbiology of the Chinese Academy of Sciences, Qilu Pharmaceutical, as well as other domestic and international biotech organizations and CROs.

A recent report by Towards Healthcare highlights that the antiviral drugs market is growing, as antiviral medications support the body in fighting off harmful viruses. These drugs simplify symptoms and cut the length of a viral infection. Antivirals reduce the risk of getting or spreading viruses that cause herpes and HIV. Several approved antivirals treat the coronavirus that causes COVID-19. Antivirals are medications that support the body in fighting off some viruses that cause disease. Antiviral drugs are also preventive. Antiviral medications help the consumer's body fight off infections. They’re like extra reinforcements that work alongside the body’s natural defenses to keep you safe from the invasive virus.