Should I Be Worried About Measles?
It goes without saying that we are hearing a lot in the news media these days about measles. It’s understandable why. A hundred years ago, infectious diseases (like measles) resulted in nearly half of all deaths in the US. The advent of antibiotics and immunizations have reduced this to less than 3% now. In fact, some of the disease have even been eliminated. Measles was one of those. Back in the day, measles used to infect 3-4 million people per year in the US. In 2000, the CDC declared that measles had been eliminated in the US, meaning that no clinical case had been contracted in the country in at least 12 months. (To be clear, there were still cases of measles being reported, but they were in travelers returning from abroad where measles had not been eliminated).
The number of cases per year in the US sat at an average of 63 per year between 2000 and 2007. In the years since, the highest number of measles cases in the US was 667 in 2014, according to the CDC. Even last year, there were 372 cases reported in the US. But year-to-date in 2019, as of May 17, there have been 880 individual cases of measles. The worst year on record since
Why Are We Seeing More Measles?
An outbreak is an epidemiological term that refers to an increase in the occurrences of a disease in a particular time and place. Outbreaks of measles have been occurring this year, and primarily start when someone becomes infected while traveling overseas in an area where measles is endemic. Measles is highly contagious, so the virus spreads rapidly from person-to-person in an unvaccinated population.
Scientists measure the transmissibility of an infection with something called the basic reproduction number, or R0 (pronounced “R nought”). The R0 estimates the number of people who can be infected by one sick person provided that the group of exposed people are not immune. Measles has one of the highest R0 at 12-18. (Consider that Ebola has a R0 1.5-2.5 and HIV has a R0 of 2-5.)
The reason for this crazy high transmissibility is that the measles virus is spread via airborne transmission. If an infected person coughs or sneezes in a room, the virus can literally persist in the airspace for up to two hours. In an unimmunized population, it is expected that up to 90% of the close contacts with the sick individual will contract measles.
The only way to contain a virus this contagious is through immunization and what scientists call herd immunity. Once enough people in a society are immune to a disease (typically through vaccination), there is an indirect protection of an outbreak occurring. There simply are not enough susceptible people to contract the infection and allow the outbreak to continue. The more contagious a disease (higher R0), the more herd immunity is needed to halt outbreaks. With measles, it’s estimated that at least 93-95% of a population needs to be vaccinated in order to eliminate endemic transmission (that means people contracting de novo cases in that population).
As our society advances, people are traveling more and more. There are pockets of measles all over the world in places that have not been able to contain the disease as well as the US. Unfortunately, concomitant with that, there are increasing pockets of unimmunized people within the US who by definition are susceptible to an outbreak. If these factors combine, then it’s a recipe for an outbreak. Currently, the CDC has identified ten such outbreaks around the US. A measles outbreak is defined by CDC as three or more cases.
What Does Measles Look Like? Do I Have Measles?
Well, first of all, it is far more likely that the rash you or your child has is from something other than measles. Yes, there has been a ton of media coverage and an increased awareness of the disease this year. But keep in mind, that here in Texas, there have only been 15 confirmed cases of measles as of May 14th.
Having said that, here is what a typical measles infection looks like. It starts with the three C’s: cough, coryza (a fancy medical term for runny nose), and conjunctivitis. A lot of viral upper respiratory conditions begin this way, making it difficult to distinguish measles at this point unless there is a history of known exposure in an unimmunized person.
Two or three days into the illness, a patient can develop tiny white spots in the mouth that are known as Koplik’s spots. In outbreak scenarios, these spots are extremely helpful because when detected they can help a clinician identify and isolate a patient with measles before they get to the peak of infectivity which occurs a few days later.
The hallmark of measles is the rash and fever which typically comes about three to five days after the onset of symptoms. The rash typically starts on the head, and moves downward, and is manifest by flat red areas (macules). As the disease progresses, these macules can join into larger macules. There can also be small raised red bumps called papules. This is why the rash is often referred to as maculopapular. Fever can be as high as 104.
As stated above, because the early symptoms can look like other viral infections, a clinician who is concerned about measles will likely ask questions that have to do with exposure and immunization status. Has the child traveled internationally? Are immunizations current? Are you in a community that has had a measles outbreak before?
If there is a suspicion of measles, the testing that has to be done is twofold. It includes a blood test, and a nasal or throat swab.
About one out of every 1,000 cases of measles can lead to encephalitis – a dangerous brain infection that if survived, can cause permanent disability. Other serious complications include pneumonia, and altogether these complications can cause one to three deaths per 1,000 cases.
The Measles Vaccine
The measles vaccine is typically given at 12-15 months of age and again at 4-6 years of age. Why don’t we give the vaccine sooner? Well, there is evidence that there is passive immunity to the virus from the child’s mother. This immunity could hinder a child’s immune response to the vaccine, making it less effective. Since this passive immunity begins to wane at around 6 months, we administer the vaccine around a year of age for better effect. About 5% of children will not be immune after that dose, which is why we give a second dose at age 4-6.
The vaccine is safe, and given the extreme transmissibility of the disease, and the potential complications, physicians (including us) strongly recommend that everyone is vaccinated.
Do I Need a Measles Vaccine Booster?
If you received two doses of the vaccine as a child, you probably do not need a booster of the measles vaccine, according to the CDC. But experts are somewhat divided on this in practice. The measles vaccine came out in 1963, and the two-dose regimen with the live virus vaccine we use now was in widespread use by 1967. It is true that anyone who received two doses after 1967 is probably good. But before that is when it gets unclear.
Between 1963 and 1967, some people received a killed-virus vaccine that was not as effective. If you might have received this vaccine, you may need a booster.
Most people born before 1957 are likely to be immune from having had measles as a child. If you aren’t sure, and you may be traveling overseas, or otherwise at high risk of being exposed to measles (like living near an outbreak), you should either be tested for immunity or simply just get the vaccine.
There is an antibody blood test that can determine for sure if you are immune to measles. However, some doctors just recommend that if you fall into the category where you are uncertain, it’s probably best to just get the vaccine. The reason here being that you avoid being stuck with a needle twice, and the unnecessary expense of the antibody test.