Are masks still effective even when many aren’t wearing them? What experts say

LOS ANGELES — Californians seem to be shedding masks at a rate not seen since last June, just before summer’s delta surge.

The odds are good that at least one person on a crowded flight would test positive for the coronavirus. In the UC San Francisco hospital system, for instance, the asymptomatic positivity rate as of Tuesday was about 2% — meaning 1 in 50 people were testing positive despite not showing any signs of illness, according to Dr. Robert Wachter, chair of the university’s Department of Medicine.

Applying that same ratio to a flight with 150 passengers would mean there’s a “95% chance that at least one passenger has COVID,” he noted on Twitter. San Francisco, Wachter added, “has a relatively low COVID rate, so odds on a U.S. flight today are likely worse.”

So what do experts say about when