First includes everybody who refuses to have their kids vaccinated for bullshit reasons*.
Second, all kinds of illegal aliens both bringing diseases in AND not being vaccinated.
California is in the midst of its worst outbreak of whooping cough in a half-century. More than 2,700 cases have been reported so far this year — eight times last year's number at this point. Seven of the victims, all infants, have died.
And here's what really worries pediatricians like USC's Harvey Karp: Doctors thought they wiped out whooping cough when they developed vaccines decades ago.
*Be it noted that some parents have reason: daughter got sick as hell after vaccinations. Not just sore at the injection site and a little fever, actually sick. Seriously at least once. So we stopped her getting those, and she's refused any such ever since.