04/16/2026
Measles cases are climbing in the U.S. again this year. I am not here to scare anyone, but it is worth understanding what this actually looks like clinically.
What is it?
Measles is caused by a paramyxovirus and is one of the most contagious infections known. If an infected person walks through a room, the virus can linger in the air for up to two hours. About 9 out of 10 unvaccinated people who are exposed will get infected.
What are the first signs?
It does not start with the rash. Symptoms show up 7 to 14 days after exposure and look like a bad upper respiratory infection: high fever (often over 104), cough, runny nose, and red watery eyes. Doctors call this the "three Cs" prodrome: cough, coryza, conjunctivitis.
About 2 to 3 days in, you may notice small white spots inside the cheeks near the back molars called Koplik spots. They look like tiny grains of salt on a red background. They are not always present, but when they are, they are essentially unique to measles and show up before the rash does.
The rash appears 3 to 5 days after the first symptoms. It starts at the face and hairline, then spreads downward over about 48 hours. By the time the rash shows up, the person has already been contagious for several days.
How is it diagnosed?
The clinical picture is usually enough to raise suspicion. Confirmation is done through blood testing for measles IgM antibodies or PCR from a throat or nasal swab.
Does the vaccine work?
One dose of MMR is about 93% effective. Two doses bring that to about 97%, and protection is considered lifelong for most people. Breakthrough infections can happen, especially during large outbreaks, but vaccinated people tend to have milder illness with fewer complications. About 3% of current cases this year are in vaccinated individuals.
Is there a treatment?
No specific antiviral. Treatment is supportive: manage the fever, stay hydrated, and watch for complications. Vitamin A is sometimes given, especially in children, because it has been shown to reduce severity.
How serious is it?
For most people, measles is miserable but self-limited. Recovery takes about 7 to 10 days. Complications happen in roughly 30% of cases overall, but the majority of those are things like ear infections and diarrhea. The serious ones are less common: pneumonia occurs in about 1 in 20 children, encephalitis in about 1 in 1,000, and death in roughly 1 to 2 per 1,000 infected children, usually from respiratory or neurologic complications.
Practical takeaway: if you have had two doses of MMR, you are very well protected.
Disclaimer: This post is for general information only and is not medical advice. If you have symptoms or questions about your health, talk with your clinician.
Learn about this vaccine-preventable disease that once was common in childhood and is known for a splotchy rash and high fever.