Measles fast facts: How contagious is it? Who’s safe? And what are symptoms?

Illinois marked its 12th confirmed measles infection Thursday, the most since 17 were reported in 2015.

Ten cases are connected with a shelter for migrants in Chicago, and experts from the U.S. Centers for Disease Control are working with city and state officials to contain the outbreak.

The 12 infections involve six children and six adults in Chicago.

The U.S. introduced a measles vaccine program in 1963, which almost eliminated the disease. In Illinois, there have been an average of 3.4 cases reported annually from 2010 through 2023 — with zero reported in six of those years.

But it was a common ailment prior to inoculations. “Most people born or living in the U.S. before 1957 are immune to measles, simply because they've already had it,” according to the Mayo Clinic.

For those unfamiliar with the virus, here are some facts and tips:

What is measles?

It’s a highly contagious respiratory disease that often results in a high fever, coughing, rash and conjunctivitis.

The virus circulates in a room for up to two hours after an infected person sneezes or coughs. The infection rate is about 90% for those who aren’t immune.

Who won’t contract measles?

Being vaccinated provides strong protection against measles, the CDC says. Two doses of the MMR vaccine are 97% effective in preventing the virus and one dose is 93% effective.

Also, anyone who already had measles is protected because the body builds up immunity fighting the disease.

If unsure about your vaccination status, check with your doctor.

What are the symptoms?

A high fever, dry cough, runny nose, sore throat, red and watery eyes, a rash, and tiny white spots inside the mouth.

How serious is a case of the measles?

There are no antibiotics for measles, but bed rest and plenty of fluids will help with a mild case. About 20% of individuals who contract measles will need to be hospitalized. Between one to three of every thousand individuals with measles will die, the CDC found.

Who is most at risk from complications of measles?

Babies and children age 5 and younger, pregnant women, and people with compromised immune systems such as those with leukemia or HIV.

Are measles’ vaccinations mandatory for children to attend school?

Illinois requires schoolchildren to be vaccinated, with medical and religious exemptions.

Sources: U.S. Centers for Disease Control, Illinois Department of Public Health, Mayo Clinic.