Health officials reported 143 measles cases in Quezon City between 1 January and 15 April, warning that nearly one-sixth of those infected are infants too young to be vaccinated.

In an advisory issued late Thursday, the local government noted that 23 of the patients are not yet eligible for the measles vaccine. These infants rely entirely on “herd immunity” — indirect protection that occurs when a large percentage of a community is vaccinated — to avoid infection.

“This means they are relying on community protection,” the city government said in a statement.

Measles, known locally as tigdas, is a highly contagious viral disease that spreads rapidly in crowded areas. While it can affect anyone, children aged 10 and younger are the most susceptible. Common symptoms include fever, cough, runny nose and distinct red rashes.