New school year, new measles outbreak?

America is in the grips of the largest measles outbreak in 25 years.

Parents and authorities nationwide are fearing that a new school year could mean more measles cases.

As of August 2019, America is in the grips of the largest measles outbreak in 25 years. The Centers for Disease Control and Prevention has reported 1,182 cases already in 2019, with 10 new cases confirmed Monday.

While the number of new cases has trended downward over the summer, experts caution parents against presuming the epidemic is over—especially as the school year gets started.

“Anytime, anywhere you have a large group of people together, especially children, there can be an outbreak of measles,” Rachel Orscheln, associate professor of Pediatric Infectious Disease at Washington University in St. Louis, said in an interview with ABC News. “One infected child can potentially affect hundreds of children...even before they begin to show symptoms of the disease.”

Measles is extremely contagious and can have devastating consequences.

One out of 1,000 measles cases will develop acute encephalitis (inflammation of the brain), which often results in permanent brain damage. One to three out of every 1,000 children who become infected with measles will die from respiratory or neurologic complications.

Once a child is over the initial illness, he or she can still face lasting consequences of a measles infection.

Measles infection can lead to “immune amnesia,” when the disease weakens the body's defenses against other diseases.

A rare but fatal degenerative disease of the central nervous system, SSPE (subacute sclerosing panencephalitis) can develop seven to 10 years after a measles infection.

If unvaccinated children are around a person with measles, they have at least a 90% chance of becoming infected. The MMR vaccination is extremely good at preventing measles -- just one dose is 93% effective in preventing measles while two doses offer 97% protection. If your child has been vaccinated, it's likely that he or she is protected against the disease.

Dr. Áine Cooke is a Senior Pediatric Resident at Washington University in St. Louis and a member of the ABC News Medical Unit.