There have been 23 confirmed cases of measles since December 2023.

The Centers for Disease Control and Prevention (CDC) is warning clinicians to remain on alert for measles cases due to a growing number of infections.

Between Dec. 1, 2023, and Jan. 23, 2024, there have been 23 confirmed cases of measles including seven cases from international travelers and two outbreaks with five or more infections each, according to an email sent this week.

Cases have been reported in Pennsylvania, New Jersey, Delaware and the Washington, D.C. area so far.

Most of these cases were among children and adolescents who had not been vaccinated against measles, despite being eligible.