For months, public health experts have been eagerly watching the companies developing spit tests for the coronavirus that could be used at home, producing results in a matter of minutes.

In the last week, leading epidemiologists from respected institutions have, through different methods, reached the same conclusion: About 85 to 90 percent of the American population is still susceptible to SARS-CoV-2, the virus causing the current pandemic.

The number is important because it means that “herd immunity” — the point at which a disease stops spreading because nearly everyone in a population has contracted it — is still very far off.