Measles – What’s Old Is New Again

Written by Hannah Harp 

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Measles is back. This article reviews its clinical presentation, complications, and vaccine recommendations.

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We’ve covered measles before. So far in 2025 (last updated May 1), we have had  935 confirmed measles cases in the US. 13% have required hospitalization, and 3 cases have ended in death. With all of the politicization and misinformation going around, this timely review gives you what you need to know. Take home: contact your local health department so that you have a workflow in place in case of a suspected measles case!

Basic facts: measles is an extremely contagious RNA virus, with R₀ of 18. It has airborne, droplet, and contact transmission. Incubation period is 8-21 days.
Presentation: Luckily, measles has a characteristic presentation. Two to four days of fever (often >40ºC), brassy cough, clear rhinorrhea, and impressive non-purulent conjunctivitis. Rash appears about two weeks after exposure – a morbilliform rash starting along the hairline before moving down to the body and out to the extremities. Fevers generally resolve a few days after the appearance of the exanthem. The rash lasts about a week, while the cough lasts 10-14 days. Koplik spots (white macule on red base on buccal mucosa) are pathognomonic, but they last only 2-3 days and often have resolved by the time a patient presents for care. Patients remain contagious for four days after the start of the rash.
Managing suspected cases: Patients should be masked and placed in an airborne isolation room or a closed room. Local or state department of health should be called for real-time guidance about testing and transfer to a facility with airborne isolation rooms. Preferred testing is PCR testing by NP or pharyngeal swab and is usually handled by the department of health lab.
Potential complications: Most cases are uncomplicated. The most common complication is pulmonary involvement (>50% of cases), followed by secondary bacterial infections (AOM, pneumonia, and tracheitis). Immune dysregulation following measles infection is well-described, but poorly understood. Myocarditis, pericarditis, blindness, and purpura are less common complications. As for CNS complications, encephalitis (direct viral encephalitis or ADEM) is most common (1:1000), while subacute acloerosing panencephalitis (SSPE) occurs years after measles infection and is nearly universally fatal. This complication is much more common in patients who contract measles before the age of 1 year (1:600), but is otherwise very rare (1:100,000).
Vaccine review: There are two doses of the live attenuated vaccine in the primary series, traditionally administered at 1 and 4 years of age. One dose of vaccine has 93% effectiveness, while two doses have 97% effectiveness. Follow your state or local health department recommendations for off-schedule dosing during an outbreak.

How will this change my practice? 
We don’t have any old hands at our clinic who have experience with measles, so this review is extremely helpful! I think it also will be helpful when addressing vaccine hesitancy to have some of these complication stats on hand.

Source
What’s Old Is New Again: Measles. Pediatrics. 2025 Apr 11. doi: 10.1542/peds.2025-071332. Epub ahead of print. PMID: 40211105