The world knows SARS-CoV-2 intimately now, but there are more than 200 virus species capable of infecting humans and causing disease. And they all want to do the same thing: Invade the host cells, hijack each cell’s machinery and reproduce. The human immune response system has numerous levels of robust defense, but many invading pathogens—as we are seeing now with the Omicron variant—have a way to break through.