Measles

What is measles?

Measles is a highly contagious virus that causes infection (also called measles). Because it is so contagious, most people who have not yet been infected or vaccinated who are exposed to someone infected with the virus will develop measles.

How is measles transmitted?

Measles is spread by direct contact with respiratory droplets (spit/saliva/secretions emitted when someone who is infected talks, coughs or sneezes) and also by airborne routes (meaning that the virus can be suspended in the air and can expose people who are in the same room even if not close by or even by entering the room after the infected person has left until there has been enough air exchanges to remove all the virus).

What is the typical case of measles like?

Often a person who is infected will begin to feel very tired and easily fatigued, lose their appetite, begin to experience fever, will develop a runny nose and cough and pinkeye. Several days later, a red rash erupts, usually on the face, but gradually spreading down the body over the chest and abdomen, the arms and legs. The rash will often involve the palms of the hands and the soles of the feet. Patients often feel the worst during the first couple of days of the rash. In uncomplicated cases, patients tend to start to feel better and have resolution of the fever several days after the rash begins. The cough is usually the last symptom to resolve.

Why try to prevent cases of measles?

While many people recover uneventfully from measles, there are many alarming potential complications of measles and other than knowing that older individuals and those that are immunocompromised are more likely to develop severe disease and complications, we cannot predict which children will develop potentially life-threatening complications.

Prior to the availability of a vaccine, there would be as many as half a million cases of measles each year in the U.S. After vaccines were widely available, cases of measles in the U.S. were as low as 100 in a year. In the early 1960s, prior to the availability of the measles vaccine, roughly 8 million children world-wide would die of measles complications every year.

What are the complications that can occur after measles infection?

One of the most common and also unique complications of measles infection is what is referred to as “immune amnesia,” meaning that there is a loss of some of the immune protection the person had already built up prior to getting infected with measles either due to vaccination or due to prior infection. Researchers had noted that in the few years following measles infection, children seemed to have higher rates of infection and even more severe outcomes. When looking into why, they discovered that the measles virus is able to use a receptor on certain immune cells of the body to infect the very cells that produce antibodies and are meant to protect us from infection. Following measles, the researchers found that persons could lose anywhere from 11 to 73 percent of their preexisting antibodies to both viral and bacterial infections and that this loss of immune protection could last as long as three years. If you want more details, see https://www.science.org/doi/10.1126/science.aay6485.

The most common acute complications involve the lungs and the brain. Pneumonia accounts for about 60 percent of the deaths in infants with measles. Pneumonia can be caused directly by the measles virus or can be a result of a superimposed bacterial infection due to the damage caused by the measles virus that can facilitate bacteria invading the damaged lungs.

The brain complications most often manifest as a condition referred to as encephalitis (meaning an inflammation of the brain), and can take one of two forms. Acute (meaning occurring during the measles illness rather than after it) encephalitis is often recognized by a recurrence of the fever or fever that doesn’t resolve in the normal timeframe, along with headaches, seizures, and a change to the level of consciousness (less alert, confused, etc.). While most people survive this complication, prior to vaccines, some individuals would be left with deafness, blindness or other permanent brain dysfunction.

An even more dreaded, but fortunately rare, complication of measles is subacute sclerosing panencephalitis (SSPE), the other form of encephalitis, but unlike the acute encephalitis above, this encephalitis does not have its onset until years after the person has seemed to have fully recovered and it is uniformly fatal. Typically, others will note personality changes, the patient’s handwriting begins to clearly deteriorate, and they become forgetful. As the condition progresses, the patient becomes progressively less able to walk, stand, and even talk. The patient may become combative, begin to have seizures and eventually lapses into a coma.

Is the measles vaccine safe and effective?

Getting the measles vaccine to prevent measles infection is generally safer than getting the measles infection itself. The measles vaccine is highly effective and like the infection itself, confers life-long protection for most people. However, one of the ways this is achieved is by using the actual measles virus but pre-treating it so that it is in a weakened (attenuated) form. For healthy children and adults, the vaccine will not cause the measles disease and therefore will prevent the various complications from occurring. However, because the virus is not killed, the vaccine is generally not advised for people whose immune systems are weakened or otherwise compromised.

The vaccine is highly effective. A single dose is 93 percent effective on average at preventing measles and a second dose increases effectiveness to 97 percent on average.

The following graph depicts the cases of measles in the U.S. before and after the measles vaccine was made available (1963):

For details on the safety of the measles vaccine, see https://www.cdc.gov/vaccine-safety/vaccines/mmr.html.