San Francisco is one of many municipalities where this is taking place. Minor consent exceptions exist in Alabama, Alaska, Arkansas, Delaware, Idaho, Illinois, Kansas,
Louisiana, Maine, Massachusetts, Montana, Nevada, Oregon, Pennsylvania, South Carolina, Tennessee, Washington and West Virginia, as well as Washington D.C.
Because the current Moderna, Pfizer, and J&J vaccines have been only authorized by the FDA under Emergency Use Authorization (EUA), the safety and effectiveness data are still being collected. This means the current mass vaccination program is an experiment in an on-going study in which researchers may still find small effect-size side effects.
It is a fact that vaccines that receive EUA are considered experimental until the FDA formally approves it as it is entirely possible that a rare side effect will be found after mass vaccination allows a longer term of observation on a larger number of people.