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Measles

Calypta Health Disease Information Statement
  • A highly contagious virus. Infects nine in ten non-immune people in close contact with someone who has it. 1
  • Spreads through the air. Coughing and sneezing send it into the air where it can linger for hours. 2
  • High fever, cough, runny nose, red eyes, then a rash starting at the hairline that spreads over the whole body. 3
  • A miserable week or more. Fever can go above 104°F, and children are typically sick for seven to ten days. 4
  • Weakens the immune system by erasing some memory of prior infections, so kids get sick more easily for years. 5
  • Spreading again in the U.S. Very rare for decades, then thousands of cases reported in 2025 and 2026. 6
  • The MMR vaccine provides long-lasting immunity to measles. Two doses cut the risk by about 97%. 7

Of 10,000 children who get measles

* Based on CDC estimates of rates among reported cases. 13

Of 10,000 children who get the MMR vaccine

~3 have a serious side effect† 14

† Fever or a mild rash after the vaccine is common and short-lived. 19

≪1 means much less than one per 10,000. 17

Disease Information Statement · Measles · September 2026 © 2026 Calypta Health
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Sources

Based on the versions of these sources published as of September 10, 2026.

  1. 1. A highly contagious virus. Infects nine in ten non-immune people in close contact with someone who has it.

    CDC: “If you have measles, up to 90% of the people close to you, who are not immune, will also become infected.” Pink Book: “more than 90% secondary attack rates among exposed susceptible persons in close-contact settings.” This is the attack rate among susceptible close contacts, mostly household; the risk from briefer or more distant exposure is lower.

  2. 2. Spreads through the air. Coughing and sneezing send it into the air where it can linger for hours.

    CDC: “It can spread to others through coughing and sneezing,” and “Measles can live for up to 2 hours in an airspace after an infected person leaves an area.”

  3. 3. High fever, cough, runny nose, red eyes, then a rash starting at the hairline that spreads over the whole body.

    CDC: “High fever (may spike to more than 104°),” “Cough,” “Runny nose,” “Red, watery eyes,” then “Measles rash appears 3 to 5 days after the first symptoms. It usually begins as flat red spots that appear on the face at the hairline. They then spread downward to the neck, trunk, arms, legs, and feet.”

  4. 4. A miserable week or more. Fever can go above 104°F, and children are typically sick for seven to ten days.

    CDC: “High fever (may spike to more than 104°).” Pink Book: “The prodrome lasts 2 to 4 days” and “The measles rash is a maculopapular eruption that usually lasts 5 to 6 days.” Together, seven to ten days.

  5. 5. Weakens the immune system by erasing some memory of prior infections, so kids get sick more easily for years.

    Mina 2015: “measles has a more prolonged effect on host resistance, extending over 2 to 3 years.” Mina 2019: “Measles caused elimination of 11 to 73% of the antibody repertoire across individuals.” Petrova 2019: “immunosuppression can persist for months to years after infection, resulting in increased incidence of secondary infections.”

  6. 6. Spreading again in the U.S. Very rare for decades, then thousands of cases reported in 2025 and 2026.

    CDC: “Measles was declared eliminated from the United States in 2000.” CDC counts 2,289 confirmed cases in 2025 and 3,134 in 2026 through September 3.

  7. 7. The MMR vaccine provides long-lasting immunity to measles. Two doses cut the risk by about 97%.

    CDC: “Two doses of measles vaccine are 97% (range: 67% to 100%) effective at preventing measles. One dose is 93% (range: 39% to 100%) effective at preventing measles.” Effectiveness is the reduction in risk among vaccinated people relative to unvaccinated people. Pink Book: vaccine-induced immunity “appears to be long-term and probably lifelong in most persons,” and waning “appears to occur rarely and to play only a minor role in measles transmission and outbreaks.”

  8. 8. ~2,000 are hospitalized or worse~2,000 hospitalized

    CDC: “About 1 in 5 unvaccinated people in the U.S. who get measles is hospitalized,” or 2,000 per 10,000. This rate is for all reported infections; CDC gives no rate specifically for children. Between 2001 and 2022, the overall hospitalization rate was 18%. In 2025, seven in ten of the reported measles cases were in people under 20, and the hospitalization rate was 11% overall, 18% for children under 5 and 12% for adults. “Or worse”: some of those who are hospitalized die.

  9. 9. ~500 pneumonia

    CDC: “As many as 1 out of every 20 children with measles gets pneumonia,” or 500 per 10,000. “As many as” makes this an upper estimate.

  10. 10. ~10 brain swelling (encephalitis)

    CDC: “About 1 child out of every 1,000 who get measles will develop encephalitis (swelling of the brain),” or 10 per 10,000.

  11. 11. ~20 deaths, most often from pneumonia

    CDC: “Nearly 1 to 3 of every 1,000 children who become infected with measles will die from respiratory and neurologic complications,” or 10 to 30 per 10,000. CDC calls pneumonia “the most common cause of death from measles in young children.”

  12. 12. ~1 death from SSPE years later; caused by virus persisting in the brain

    CDC: 7 to 11 SSPE cases per 100,000 measles cases, or 0.7 to 1.1 per 10,000, with onset that “generally develops 7 to 10 years” after infection. The National Institute of Neurological Disorders and Stroke describes SSPE as a “slow, but persistent, viral infection” of the brain. Wendorf 2017 found higher rates for infection in early childhood: 1 in 1,367 before age five, about 7 per 10,000, and 1 in 609 under 12 months, about 16 per 10,000. We use the more conservative CDC figure; the higher estimates rest on small numbers of cases.

  13. 13. Based on CDC estimates of rates among reported cases.

    The figures are CDC rates among reported cases, rounded to a count per 10,000. Some infections go unreported, so rates among everyone who catches measles may be somewhat lower.

  14. 14. ~3 have a serious side effect

    The sum of the three serious events beneath: 2.5 to 3.3 febrile seizures, 0.25 low platelet counts, and 0.02 to 0.14 anaphylaxis, or 2.8 to 3.7 per 10,000. The events are rare enough that overlap is negligible.

  15. 15. ~3 fever seizure, no lasting harm

    CDC: febrile seizure in “about 1 in 3,000 to 4,000 children” under seven in the 6 to 14 days after MMR, or 2.5 to 3.3 per 10,000. “Febrile seizures following MMR vaccination are rare and are not associated with any long-term effects.”

  16. 16. <1 temporary low platelet count; can cause unusual bruising or bleeding

    CDC: immune thrombocytopenic purpura in about 1 per 40,000 vaccinated children in the six weeks after MMR, or 0.25 per 10,000. MMR “rarely causes a temporary low platelet count, which can cause a bleeding disorder that usually goes away without treatment and is not life threatening.” Pink Book: “The clinical course of these cases is usually transient and benign.”

  17. 17. ≪1 severe allergic reaction≪1 means much less than one per 10,000.

    Pink Book: “Immediate, anaphylactic reactions to MMR vaccine occur in 1.8 to 14.4 cases per million doses,” or 0.02 to 0.14 per 10,000.

  18. 18. 0 deaths

    Death is not impossible, but it is vanishingly unlikely. CDC: measles inclusion body encephalitis “almost always happens in patients with weakened immune systems,” and “There have been three published reports of this complication happening to people who are vaccinated. In these cases, encephalitis developed between 4 and 9 months after MMR vaccination. In one case, the measles vaccine strain was identified as the cause.” Costales 2022 reports a second sequence-confirmed vaccine-strain case, fatal, after MMRV (ProQuad) in a child with leukemia. IOM 1994, on deaths after measles vaccine: “No relative risk can be calculated”; the risk is “extraordinarily low.” Two confirmed cases against the millions of doses given every year is far below one per 10,000.

  19. 19. Fever or a mild rash after the vaccine is common and short-lived.

    Pink Book: “After MMR vaccination, 5% to 15% of susceptible persons develop a temperature of 103°F (39.4°C) or higher,” and “MMR vaccine may cause a transient rash in approximately 5% of vaccine recipients.” CDC lists “Fever” and “Mild rash” among common side effects.

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An information sheet from Calypta Health · © 2026 Calypta Systems

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