When a new virus starts spreading, scientists scramble to find drugs that can fight it. But here's the problem: building a big collection of promising compounds to test can take years. That's the bottleneck researchers at Simon Fraser University in British Columbia, Canada, just broke through. A team there has invented a new method that uses light to build enormous libraries of antiviral compounds in just weeks instead of months or years. Their work was published in the journal Science. Nucleoside analogs, the compounds at the center of this research, are molecules that mimic the building blocks of DNA and RNA. Drugs made from them already treat conditions like HIV, hepatitis, and certain cancers. The challenge has always been making enough different versions to test. With the new light-driven approach, scientists can start with one simple molecule and quickly attach different nucleobases'' to it — the parts that give DNA its specific instructions. The team generated a library of more than 70 different compounds this way. To see if it worked, they tested the library against HIV. Three of those compounds showed activity on par with drugs already approved to treat the disease. Most of the compounds in our library were entirely new,'' said Robert Britton, a professor of chemistry at Simon Fraser University who led the research. A few had been made before, but it took other groups longer to synthesize those molecules, and they were not able to modify and improve them as readily.'' The research also included scientists from the drug company Merck. Britton said the method could be a game changer when a new outbreak emerges. The more compounds you can screen, the better your chances of finding something effective,'' he explained. ``With this method, we can produce libraries 10 to 100 times larger in just weeks, rather than months or years.'' The team is now working to expand the library even further and test it against other viruses, with the goal of getting ahead of the next global health threat.