You probably know there is an ongoing outbreak of measles in the United States, Canada, and Mexico, but did you know that there are several different diseases with “measles” in their everyday name?
The disease “measles” is caused by a virus. A virus is a tiny particle stuffed with its own instruction booklet on how to make copies of itself. The instructions are written in either DNA or RNA language, depending which type of virus it is. Just like food recipes, the instructions for each virus are unique and equip the virus with different ways to infect the body and cause disease. Even if they’re different, many viruses can cause shared symptoms like rashes.
Image credit: Elliot Wish
For example, there are in fact three different viruses that people sometimes refer to with names that include “measles”. These cause diseases known as Rubella, Rubeola, and Roseola. Fortunately, the measles virus and Rubella virus are part of the Measles, Mumps, and Rubella (MMR) vaccine. People who received the MMR vaccine are strongly protected against both diseases.
What are these viruses? Let’s break it down.
Rubeola (roo-bee-oh-luh) = Measles
The childhood disease most commonly referred to as measles is formally known as Rubeola and is responsible for the large, ongoing, outbreak that began in West Texas earlier in 2025.
🦠 Virus name: Measles virus
🌡️ Disease name: Rubeola or Measles
📃 Instruction language/virus type: RNA
🤒 Common symptoms: Usually begins with high fever, cough, and white spots in the throat (Koplik’s spots). A rash appears 3-5 days later and begins on the face or neck before spreading to the entire body. Once a person is exposed to (breathes in) the virus, it can take up to 15 days for symptoms to appear.
💉 Vaccine availability: The first “M” in the Measles, Mumps, and Rubella (MMR) vaccine, which was first introduced in 1969. With two doses, the measles vaccine provides strong protection, especially against severe disease. Why does the vaccine work so well? One reason is because it can take two to three weeks for symptoms to develop in the exposed person. This is enough time for that person’s immune system to ramp up protection from the memory stored after the vaccine. This allows the body to stop the virus before it causes disease. Rapid elimination of the virus also prevents the virus from making copies of itself and spreading to others.
💉 Vaccine impact: Once the vaccine was introduced, the number of measles cases was reduced by over 99%. The CDC declared Rubeola disease eliminated in the US in 2000 due to the successful immunization campaign. This means that most cases happen in unvaccinated people who got the virus while they were outside of the US. Unfortunately, there is an ongoing outbreak of measles this year, leading to a large increase in cases as discussed in previous posts. See here and here.
😷 Transmission: A person can spread the disease by breathing, coughing, or sneezing small respiratory droplets into the air from four days before to four days after they develop a rash. The virus-containing droplets remain suspended in the air (don’t fall onto surfaces) for several hours. Measles virus is one of the most infectious viruses we know about. Let’s say there was a room of 100 unvaccinated people and one infected person walks in and breathes out virus. We can expect that 90 of those 100 people will develop measles. That is why it is important for health departments to announce exposures, especially where lots of people were exposed. If you want to keep track of measles cases and exposures, you can check out this good site[archived link].
🤢 Complications from infection: Many children who develop measles recover and do just fine, but the measles virus is sneaky and can harm the immune system and make the child more likely to get other infections. Some people refer to this as immune amnesia. Normally, your body makes memory B cells that help it quickly respond when they detect something from a prior infection or vaccine. Measles erases some of these cells, reducing the effectiveness of that “immune memory”, and leaving people at risk for infections they should be protected against. In addition, up to 20% of children who get measles will be hospitalized for severe disease. Complications that result in severe disease include pneumonia and swelling of the brain. Brain swelling can lead to permanent brain damage or even death.
Rubella (roo-beh-luh)
🦠 Virus name: Rubella virus
🌡️ Disease name: Rubella, “German Measles” or “Three-day measles”
📃 Instruction language/virus type: RNA
🤒 Common symptoms: Often begins with low grade fever, cough, and sore throat, but in young children a rash is often the first noticeable symptom. The Rubella rash begins on the face or neck and spreads across the whole body. Once a person is exposed, it can take from 12-23 days for the first symptoms to occur.
💉 Vaccine availability: The “R” in the “MMR” vaccine. With two doses, the vaccine provides very strong protection. We know this vaccine works particularly well because the number of Rubella cases per year in the US has hovered around 10 since the introduction of the vaccine.
💉 Vaccine impact: After introduction of the vaccine, the number of Rubella cases dropped by over 99%. The CDC declared Rubella disease eliminated in the US in 2004.
😷 Transmission: An infected person spreads the disease by coughing out or sneezing respiratory droplets containing the virus. Most infected people are contagious before the rash appears. While Rubella virus isn’t quite as easily spread as measles virus, it is still highly contagious.
🤢 Complications from infection: The people most at risk for serious complications due to Rubella virus are pregnant people. If unvaccinated people are infected during pregnancy, they can pass the virus to the fetus, which can cause loss of the fetus or congenital rubella syndrome. Children born with congenital rubella syndrome have serious birth defects [archived link], including deafness, vision problems, congenital heart disease, and developmental delays. Sadly, infection in the first trimester, a time when sometimes the person doesn’t realize they are pregnant yet, has a 90% chance of leading to these birth defects. The risk is still 1 in 5 up to the end of the second trimester. The best way to protect unborn children is to get the vaccine before becoming pregnant, because the vaccine should not be given to people who are already pregnant.
Roseola (row-zee-oh-luh) = “Baby measles”
🦠 Virus name: Roseola
🌡️ Disease name: Roseola, “Baby measles”, “Sixth disease”. “Roseola infantum”
📃 Instruction language/virus type: DNA
🤒 Common symptoms: The first symptom is usually a very high fever (103 to 105 degrees Fahrenheit or 39.5 to 40.5 degrees Celsius) that can last for 3-4 days. After the fever goes away, a rash appears. Roseola rash often begins on the tummy or back and spreads out to the entire body. The rash goes away in a few days. Most children have had Roseola by the age of two. It is important that any child who develops a rash be seen by their pediatrician to rule out the more serious Rubeola or Rubella infections. Fever can begin anywhere from 5-15 days after exposure to the virus.
💉 Vaccine availability: No vaccine
😷 Transmission: Breathing in respiratory droplets that were coughed or sneezed out by an infected person.
🤢 Complications from infection: Some children can develop seizures, called febrile seizures, when they develop such high fevers during infection.
Bottom line, there are many different viruses that can cause a measles-like rash. Fortunately, Rubeola and Rubella are covered by the MMR vaccine. Since it can be hard to tell apart the rashes caused by viruses, it is always best to check with your trusted clinician if your child, or a family member, develops a rash. The best way to protect you and your family is to stay up to date on your vaccines.
Stay well and rash-free,
Those Nerdy Girls
Want to know more?
Rubeola virus and Measles:
National Foundation for Infectious Diseases Explainer for Measles [archive link]
CDC website on Rubeola [archived link]
Rubella virus:
National Foundation for Infectious Diseases Explainer for Rubella [archived link]
CDC website on Rubella [archived link]
Mount Sinai website on Congenital Rubella Syndrome [archived link]
Roseola virus:
Cleveland Clinic website on Roseola infection [archived link]
