Chicago health workers have vaccinated hundreds of shelter residents, as Arizona health officials investigate cases near Flagstaff.
Illinois and California are among 17 US jurisdictions that have reported measles cases this year.
The CDC said today that it has received reports of 45 cases from 17 jurisdictions so far this year.
Michigan has reported 2 more cases from 2 different counties, part of a small but steady rise in US cases.
Also, Florida and Ohio have reported more cases.
So far, 15 US jurisdictions have reported 35 cases this year, including 15 in just the last week.
In other US measles developments, Arizona's Maricopa County reported two more cases.
The infections are occurring amid a global rise in cases and gaps in MMR vaccination.
Several states have now reported cases amid a global spike in measles activity.
Increased activity continues into the new year, with gaps in vaccine coverage and the season's peak still ahead.
