The flu virus has a small window of vulnerability when it tries to escape from an infected cell. A new class of experimental compounds doesn’t just block that window — it welds it shut.

Researchers from Leiden University, the University of York, the University of Barcelona, and the Francis Crick Institute have developed molecules called “sugar aziridines” that form permanent bonds with a key flu enzyme, potentially offering a new weapon against seasonal influenza and future pandemics. The findings were published March 24 in the Proceedings of the National Academy of Sciences.

A More Durable Lock

Here’s the problem with current flu drugs: they’re renters, not owners. Medications like oseltamivir (Tamiflu) temporarily block neuraminidase, the enzyme that flu viruses use to break free from infected cells and spread. The bond is reversible. Given enough time, the drug drifts away, and the virus can resume its work.

The new compounds take a different approach. They mimic a fleeting moment in the enzyme’s chemical reaction — the transition state — which allows them to bind exceptionally tightly. Then, unlike existing drugs, they form a covalent bond: a permanent molecular handshake that locks neuraminidase in an inactive state.

“Our combined study let us watch these molecules ‘shut down’ neuraminidase at the atomic level — first by fitting the enzyme’s transition state, then by enabling a covalent lock,” said Professor Carme Rovira of the University of Barcelona.

The research team achieved this by modifying the Tamiflu molecule itself, replacing a small chemical group with a reactive aziridine ring. This “warhead” enables the permanent bond that existing drugs can’t form.

Tested Against Seasonal and Bird Flu

In laboratory tests following World Health Organization guidelines, several of the compounds strongly blocked flu viruses from infecting cells. They were particularly effective against H3N2, one of the main culprits behind seasonal flu. But they also inhibited neuraminidase from H5N1 — avian influenza, or bird flu.

That last point matters. H5N1 has been spreading through wild birds and farm animals globally, with more than 70 human cases reported in the United States since 2022, including two deaths, according to Washington University School of Medicine. While the virus doesn’t yet spread easily between people, scientists warn it could adapt. Having antivirals that work against it before a pandemic hits is the kind of preparation public health officials have been urging.

Beyond Treatment: Research and Vaccines

The compounds have another trick up their molecular sleeve. Because they bind permanently to neuraminidase, they can serve as imaging probes — allowing scientists to label, track, and measure the enzyme in complex samples, including seasonal flu vaccines. This could help improve vaccine quality control by providing better tools to measure neuraminidase content and activity, a key factor in how well vaccines protect.

A Long Road Ahead

For now, these remain laboratory discoveries, not medicine cabinet fixtures. The compounds are in the research phase and will need extensive safety and efficacy testing in animals and humans before they could reach patients.

“Drug development is a lengthy and costly route where failure is more likely than success,” acknowledged Professor Hermen Overkleeft of Leiden University. “Yet the unique mode of action of our sugar aziridines… gives us a real edge over competing solutions.”

The team has filed patent applications and expressed interest in pursuing clinical development. But they’re not making promises about timelines.

Why This Matters Now

Seasonal influenza infects roughly one billion people each year and causes between 290,000 and 650,000 respiratory deaths annually, according to the World Health Organization. Resistance to antivirals is a persistent concern — one the WHO monitors through its Global Influenza Surveillance and Response System.

What makes this research notable isn’t alarm about an imminent threat. It’s the opposite. This is scientists building tools before they’re urgently needed. The next flu pandemic may be years away, or it may be closer than anyone would like. Either way, having a new class of antivirals in the pipeline is the kind of insurance that’s hard to argue against.

Sources