Acute measles in the emergency department, once a rarity, is now a reality. This means it is time for all departments to dust off old protocols for its immediate treatment and subsequent management. The good news — and the bad — is that little has changed over the intervening decades of measles eradication. However, the quiver of effective treatments, from back in the days when universal vaccination had not yet taken root, remains fairly empty.

The first, and simplest, concern following identification of acute measles in the emergency department is isolation. The most cited basic reproduction number for measles virus is in the 12 to 18 range, although variability exists beyond that general estimate. This reproduction number represents a rough proxy for the practical infectivity of a virus, and the measles virus shows dramatically greater transmission than its common comparators.

For example, SARS-CoV-2, the world-altering scourge, carried R0 estimates of generally between 2 to 4, while varicella is approximately 9, mumps and rubella around 7, and poliomyelitis around 5. Isolation in a negative-pressure room is necessary to minimize risk of transmission, accompanied by fit-tested respiratory masks such as N95 or P2.

For the vast majority of identified measles cases, nonspecific supportive care will be the only necessary treatment. For ambulatory patients not displaying any signs of dehydration, pneumonia, or encephalitis, no immediate treatment is universally indicated. The most commonly cited treatment for acute measles, if any is deemed appropriate, is vitamin A.

High-quality randomized controlled trial evidence exists regarding the benefit of vitamin A supplementation in measles, with the effect most prominently seen in patients with vitamin A deficiency. Most children and adults in the United States should not be expected to be suffering from vitamin A deficiency, in contrast to those living in resource-limited countries. Due to the beneficial effects seen, however, the American Academy of Pediatrics (AAP) and the Centers for Disease Control and Prevention (CDC) offer strong recommendations to provide vitamin A in patients being hospitalized for severe measles, regardless of suspected nutritional status.

Useful evidence to support vitamin A in non-severe measles is substantially less robust, but supplementation is unlikely to be harmful at the recommended doses. Excessive vitamin A can result in a range of toxic effects, and should therefore be limited to the recommended doses:

• 50,000 IU for infants younger than 6 months of age
• 100,000 IU for infants 6–11 months of age
• 200,000 IU for children 12 months of age and older

An initial dose can be provided immediately upon diagnosis, and the treatment course concludes with a second dose repeated the following day.