Cocrystal Pharma Tests First-Ever Norovirus Pill in Human Trials

BOTHELL, Wash. – March 31, 2026 – Clinical-stage biotechnology company Cocrystal Pharma has initiated a crucial human challenge study for CDI-988, a first-of-its-kind oral antiviral candidate aimed at treating and preventing norovirus. The announcement, made alongside the company's 2025 financial results, marks a significant step toward addressing a rampant global health issue that currently has no approved vaccine or treatment.

Norovirus, often called the 'winter vomiting bug,' is infamous for causing debilitating acute gastroenteritis, leading to an estimated 685 million cases and a staggering $60 billion in economic burden worldwide each year. As the first subjects are dosed in a highly controlled study at Emory University School of Medicine, the biotech firm is placing a major bet on its lead candidate to fill this massive therapeutic void.

A New Front Against a Pervasive Virus

The Phase 1b trial represents a critical milestone for both the company and public health. In this randomized, double-blind, placebo-controlled study, up to 40 healthy volunteers will be intentionally inoculated with the GII.2 (Snow Mountain Virus) norovirus strain. Subsequent cohorts will receive either CDI-988 or a placebo to test the drug's efficacy in preventing clinical symptoms and reducing viral shedding.

“We are delighted to report that our norovirus human challenge study evaluating efficacy and safety of CDI‑988 is underway at Emory University School of Medicine,” said Sam Lee, Ph.D., President and co‑CEO of Cocrystal. “In our first cohort, healthy subjects are being inoculated with the GII.2 (Snow Mountain Virus) strain under highly controlled conditions.”

Developing an effective countermeasure has historically been difficult due to the virus's high genetic diversity. Cocrystal believes its proprietary structure-based drug discovery platform gives it an edge. CDI-988 is a direct-acting antiviral that targets the 3CL protease, a critical enzyme for viral replication. This target region is highly conserved across all known norovirus strains, suggesting the drug could be a 'pan-viral' solution, maintaining effectiveness even as the virus mutates. Preclinical data has already shown CDI-988's activity against prevalent strains, including GII.17, which dominated in 2024-2025.

“Norovirus outbreaks can strike at any time of year in semi-closed environments such as cruise ships, military settings, and healthcare and assisted-living facilities,” stated James Martin, Cocrystal's CFO and co-CEO. “This constant threat underscores the need for an effective oral treatment and preventive that can be deployed whenever and wherever norovirus infections emerge.”

While CDI-988 is the first oral antiviral to enter such trials, the field is not without activity. Moderna is advancing a vaccine candidate through Phase 3 trials, and Vaxart is developing an oral tablet vaccine. However, Cocrystal's approach as a post-exposure treatment and prophylaxis offers a different and potentially complementary strategy to combat outbreaks.

Navigating the Biotech Gauntlet

The promising advance of CDI-988 comes as the company demonstrates increased financial discipline. Cocrystal reported a net loss of $8.8 million for 2025, a significant improvement from the $17.5 million loss recorded in 2024. This was largely driven by a sharp decrease in research and development expenses, which fell from $12.5 million to $5.1 million.

The reduction in spending is partly linked to challenges in another area of the company's pipeline. An initial Phase 2a study for its influenza A candidate, CC-42344, was completed in November 2025. While the drug showed a favorable safety profile, the company stated that efficacy analyses could not be reported due to unspecified “issues with trial conduct.” This setback necessitates an additional Phase 2a study, delaying the program's timeline and underscoring the inherent risks of clinical development.

Financially, the company ended 2025 with $7.7 million in unrestricted cash, down from $9.9 million the previous year. While the reduced burn rate signals a move toward capital preservation, the ongoing costs of clinical trials, including the new norovirus study and a planned repeat influenza trial, will continue to test its resources. This positions Cocrystal in a classic biotech balancing act: advancing a potentially game-changing lead asset while managing a constrained budget and mitigating setbacks elsewhere in its portfolio.

A Platform for Future Pandemics

Underpinning all of Cocrystal's programs is its innovative structure-based drug discovery technology. The company leverages this platform to visualize viral replication machinery at a near-atomic level, allowing it to design highly specific drugs that bind to essential, conserved sites. This method bypasses the slower, more resource-intensive process of traditional high-throughput screening.

“Developing an effective norovirus antiviral or vaccine has been challenging due to the high genetic and antigenic diversity of norovirus and lack of simple in vitro cell-based assays and animal model system,” Dr. Lee explained, highlighting how the company's technology is designed to overcome these hurdles.

The platform's potential extends well beyond norovirus. CDI-988's targeting of the 3CL protease gives it potential as a broad-spectrum antiviral against other viruses, including coronaviruses. The company remains optimistic about its viability as a future treatment for SARS-CoV-2 and other related pathogens. Similarly, its influenza candidate CC-42344 has demonstrated activity against the highly pathogenic H5N1 avian influenza strain, a virus of significant pandemic concern. Further validation of the platform's potential came in October 2025, when the company received a $500,000 NIH grant to develop a novel antiviral targeting both influenza A and B viruses.

As the human challenge study for CDI-988 progresses, its outcome will serve as a crucial validation not only for the drug itself but for the entire discovery engine behind it. Success could pave the way for a new class of targeted, mutation-resistant antivirals, while failure would represent a significant setback. For the company and the millions who suffer from norovirus annually, the results from the Atlanta-based study are eagerly awaited.