A new antiviral drug candidate, GHP-88310, has shown promise in treating measles and croup, two respiratory infections caused by a family of viruses known as orthoparamyxoviruses, researchers at Georgia State University have said. The oral, once-daily compound has been described by the scientists as the most promising inhibitor of this virus family they have encountered in years of research. Carolin Lieber, a senior postdoctoral fellow at the university’s Center for Translational Antiviral Research and lead author of the study, said the molecule represents a significant breakthrough in the search for treatments for these contagious and life-threatening illnesses.
Currently, croup – an infection of the upper airway that causes a barking cough and difficulty breathing – is managed with steroid medications, while measles can be prevented with two doses of the measles-mumps-rubella (MMR) vaccine. However, there are no federally-approved antiviral drugs specifically for measles; treatment is largely supportive and focused on relieving symptoms. For human parainfluenza virus type 3 (HPIV3), a leading cause of croup, bronchitis and pneumonia in infants, no vaccines or specific antiviral therapies exist at all. Ribavirin has shown in vitro activity against measles and HPIV3, but it is not approved for these infections, and other experimental treatments such as monoclonal antibodies remain in the laboratory and animal study phase.
The research team, led by Richard Plemper, director of the Center for Translational Antiviral Research, initially targeted HPIV3 as the primary focus for the drug, with measles identified as a secondary application. The programme was specifically designed to address the needs of vulnerable patient groups – children and the immunocompromised – who make up the majority of cases. Around three per cent of US children contract croup annually, and federal data show that most of the nearly 2,000 measles cases recorded in the United States this year are in people under 19. According to the US Centers for Disease Control and Prevention, 1,952 confirmed measles cases had been reported as of May 21, 2026, following 2,288 cases across 45 jurisdictions in 2025 – a sharp rise from 285 cases the previous year.
GHP-88310 works by blocking the machinery the virus uses to copy its genome. It is a broad-spectrum, non-nucleoside inhibitor of orthoparamyxovirus polymerases, meaning it prevents the virus from replicating its genetic material. This mechanism also helps the drug protect against viruses that attempt to evade the immune system’s defences – a challenge that has complicated efforts to treat Covid-19. The compound has demonstrated potent activity against a range of orthoparamyxoviruses, including measles virus, HPIV3, and canine distemper virus (CDV), a close relative often used as a surrogate in animal studies because measles only infects humans.
Pre-clinical results have shown that GHP-88310 is effective in both rodent and non-rodent models. In cotton rats infected with HPIV3, oral administration significantly reduced viral load in the respiratory tract. In ferrets infected with CDV, therapeutic administration resulted in complete survival, reduced viral load, and alleviation of lymphocytopenia – a drop in white blood cells that can accompany severe infections. Furthermore, the compound was found to be sterilising against HPIV3 at physiologically relevant concentrations in human airway epithelium organoids, a lab-grown model of the human airway that mimics the structure and function of the respiratory lining.
The drug has been well tolerated in animal studies. Daily doses of up to 2,000 mg per kilogram of body weight were tolerated in rats, and researchers noted a wide safety margin. “High potency and excellent tolerability ensure a very wide safety margin, which is essential for a drug candidate developed for the treatment of highly vulnerable patient groups and children,” said Plemper. The compound also exhibits improved oral efficacy and favourable tolerability in non-rodent species, expanding its therapeutic window. GHP-88310, also known by the synonym EIDD-3608, has been identified as a clinical candidate by the research team, which includes collaborators from Emory University’s Institute for Drug Development and the University of Washington Medical Center, with funding from the National Institute of Allergy and Infectious Diseases.
The development of GHP-88310 comes amid a significant resurgence of measles driven by falling vaccination rates. Measles was declared eliminated in the United States in 2000, a status that relies on maintaining vaccination coverage above 95 per cent to achieve herd immunity. “To prevent measles from spreading, about 95 per cent of the population needs to be vaccinated with the MMR vaccine,” said Jennifer Nuzzo, director of the Pandemic Center at Brown University, in an October interview. “That level of coverage creates what’s called herd immunity.” However, Nuzzo noted that the US has slipped below that threshold, standing at under 90 per cent nationally, with some communities seeing coverage as low as 35.8 per cent. The share of US counties where 95 per cent or more of kindergartners were vaccinated against measles has fallen from 50 per cent before the COVID-19 pandemic to 28 per cent. The largest single outbreak in the US since 2000 – the 2025–2026 South Carolina outbreak – involved 997 cases as of April 2026, and a separate outbreak in Texas in early 2025 led to 762 cases and three deaths.
Plemper, whose team published the research in the journal Science Advances and earlier as a preprint on bioRxiv, described orthoparamyxoviruses as “a major threat to children and vulnerable groups such as the immunocompromised.” The broad-spectrum nature of GHP-88310 suggests potential applications beyond measles and HPIV3, possibly including other viruses within the orthoparamyxovirus subfamily, such as emerging henipaviruses and mumps virus. In laboratory tests with human airway organoids, the compound achieved sterilising activity against HPIV3 at concentrations that are physiologically achievable, indicating its ability to completely eliminate the virus from infected cells.
