RIO DE JANEIRO (AP) — Brazil's health ministry has launched a nationwide vaccination campaign to protect children from measles and poliomyelitis.

The initiative follows a measles outbreak that affected over 700 people, only two years after the disease was eradicated in Latin America's largest nation. Health officials also worry that polio may return to Brazil.

The measles cases are mostly concentrated in northern states where thousands of Venezuelan refugees are crossing the border to flee economic and political hardships, as well as a failing health system. Many of them are sick and haven't been immunized.

Authorities say that Brazilians, who haven't been meeting their vaccination targets, are not prepared to receive these newcomers.

The ministry said Monday it aims to vaccinate 11.2 million children under the age of 5 by the end of the month.