this is a confusing point for a lot of people, as well. what is, again, pretty basic science suggests that you have to expel the virus somehow in order to transmit - via coughing, sneezing, etc. but, the numbers don't add up, if we assume all transmission is coming from clearly sick people.

so, what is "asymptomatic transmission"?

we had a longer than normal spring here in most of canada, and people walking around outside until fairly late into may would have experienced symptoms like runny noses that they would have normally attributed to the weather. they may have come in from outside and blown their nose, without thinking about it. or they may have even brushed their faces with their hands as they took off their hats, and then touched other people. or, maybe they weren't thorough enough with the soap on the way out of the washroom, after having touching handles and doorknobs.

this happens with other mild viruses, too - all you have to do is transmit fluids. you don't have to cough or sneeze - you could blow your nose, or just touch your face. and, you might not even be fully cognizant of what you're doing.

the truth is that these people are symptomatic, but they don't realize it or they deny it. the symptoms are so mild in many cases, that you might mistake them for allergies, fatigue, a garden variety headache or a normal reaction to cold or hot weather. so, what we call "asymptomatic" should really be replaced by "weakly symptomatic". this is no doubt the cause of the confusion...

you shouldn't be able to spread any virus without symptoms, but it's a lot harder to realize that you're symptomatic than we all think is obvious. we live in polluted cities. we're all sick all of the time.

with the warm weather, the situation flips over - instead of runny noses from the cold, you'll have sweaty foreheads from the heat. so, you may come into a grocery store from outside and wipe your sweaty brow, then touch something - without even thinking about it.

https://globalnews.ca/news/7043306/coronavirus-asymptomatic-spread-who/