It's both. There's a cluster of "crazy hippy" people in and around Marin who are convinced vaccinations are responsible for every modern ailment. I've met, and tried unsuccessfully to reason with a few of them.

The DTAP booster may be our best shot (haha) at routing around them though. Even if they won't vaccinate their children, if enough adults get regular DTAPs we might be able to get enough herd immunity that whooping cough dies out again.