Rockefeller University researchers have been able to watch a virus being built in real-time, observing hundreds of thousands of molecules assemble inside a cell to create a single particle of HIV.

They used multiple imaging techniques to record each step of the process, allowing them to watch as the virus assembled and then gradually budded off of its host cell.

Currently, much of what’s known about HIV and other viruses has been pieced together through experiments that rely on inference: microscopic and chemical probing of cells frozen in different states of viral infection.