Because if you sneeze or cough or even just breathe you are releasing fewer globs of virus goo.
Why scientists are talking about viral load and the delta variant
What sets delta apart, experts say, is how much virus is produced by those who are infected — a measure known as viral load.www.nbcnews.com
This describes how it works, but doesnt necessarily have the right conclusions on what is actually happening with the Delta strain.
In an internal document that leaked last weekfrom the Centers for Disease Control and Prevention, the agency presented data, some of which were preliminary, on the delta variant and instances where fully vaccinated individuals were infected. The CDC investigation looked at delta infections among vaccinated and unvaccinated people and found that specimen Ct values were similar for both groups.