An outbreak of measles has struck 26 people over the month since the first case was reported in Daegu on Dec. 17.
Fifteen are babies and infants and the rest are medical staff and parents. Health authorities will maintain an emergency alert for the next six weeks.
Daegu and North Gyeongsang Province saw the most infections with 17 confirmed cases, followed by Gyeonggi Province with nine, one in Siheung and eight in Ansan. All were infected with a measles strain from Southeast Asia, but none had been overseas recently. Authorities are trying to find how the virus came into the country in the first place.
Some 7,000 people are presumed to have come in contact with the patients in Daegu and North Gyeongsang Province. About 3,000 have already passed the latency period and the rest are still being monitored. In Gyeonggi Province the number is about 450 and could rise.
Symptoms include the famous dotted rash as well as cough, runny nose and high fever.
The virus spreads in the air through patients' saliva, and a single patient can infect an estimated 18 people, though many children are vaccinated.
In 2014, the World Health Organization listed Korea as having eradicated measles. But that only means that nobody was infected with a homegrown strain, not that there were no patients at all. About a dozen cases show up every year, except in 2014, when about 400 people were infected with a strain from overseas.
Infections can be avoided for life with just two MMR vaccine shots for babies, one between 12 and 15 months of age and one at between four and six. Vaccine shots for children under 12 are free.
But 14 of the 15 infants who caught measles had not been vaccinated. Some were too young, but the rest were old enough. It is unknown why the vaccine failed to work on the 15th.
Measles is relatively harmless for most children and, once over, immunizes them for life, but in some cases the illness leads to complications and even death, and it is particularly dangerous for pregnant women.