Genetic cheat code might explain why some people catch Covid but never get sick
In the earliest days of the Covid-19 pandemic, when the new coronavirus still appeared to be confined to China, public health authorities were divided over whether to declare the outbreak a global emergency. That changed once it became clear that the virus was silently spreading farther and faster than anyone realized — fueled by transmission among contagious people who didn’t feel sick.
Some viruses, like the original SARS, can only be passed when a person is showing symptoms. Others, like the flu, can be spread a day or two before symptoms appear. Studies from the first (vaccine-free) year of the pandemic suggested that more than half the cases of Covid-19 were caused by infected people who didn’t have any symptoms when they passed on the virus. Among these symptom-free spreaders, some later experienced fever, cough, and other symptoms, but about 40% never got so much as a sniffle.
