Measles: What to know about one of the most contagious diseases

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Measles cases are surfacing across Canada. Here’s what you need to know about what measles is, how it spreads and symptoms to watch out for.

What is measles?

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Measles a highly contagious respiratory illness caused by the rubeola virus. “Measles is probably the most transmissible virus affecting human beings,” said McGill University professor of medicine Dr. Brian Ward.

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Measles is airborne. It can be transmitted in schools, on buses, even during a passing interaction, Ward said. “If you’re in a Place des Arts (a major performing arts centre in Montreal) auditorium, and there’s one person at the same show as you, and they are starting to sniffle or cough or sneeze with measles, and you’re susceptible, you will probably get it.”

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Before vaccines and routine childhood immunizations were introduced, measles infected most people before the age of 20 and caused more than two million deaths worldwide each year.

How transmissible is it?

The virus lives in the nose and throat mucus of an infected person and spreads through the air when an infected person breathes, coughs, sneezes or talks. According to the U.S. Centers for Disease Control and Prevention, the virus can live for up to two hours in the airspace after an infected person leaves an area.

Infected people can transmit measles to other people from four days before, through four days after the rash appears. On average, an infected person can pass the virus on to 15 to 18 others who haven’t been vaccinated or are not immune.

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What are the symptoms and how soon do they appear?

Symptoms include a high fever, cough, runny nose, watery eyes or pink eye. They appear seven to 14 days after contact with the virus.

The telltale measles rash appears three to five days after the first symptoms and typically starts off as flat red spots on the face at the hairline, which then spread downward, from head to toe.

People are infectious before they start to show symptoms, and highly infectious for several days when they’re symptomatic, before the body takes over and clears the virus, Ward said.

Who is most at risk of complications from measles?

Infants who aren’t old enough to get the measles vaccine, kids and teens who haven’t gotten two doses of the vaccine, pregnant women and people with weak immune systems are most at risk.

Common complications in children include an ear infection and diarrhea. One in 10 may develop pneumonia. One in 1,000 can developed post-infectious encephalomyelitis, or swelling of the brain, that can lead to permanent neurological deficits like deafness, paralysis or difficulty thinking or speaking.

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One to three of every 1,000 children infected will die from respiratory or neurological complications.

How effective is the MMR (measles, mumps and rubella) vaccine?

A single dose is about 93 per cent effective against measles; two doses starting after 12 months are about 96 to 97 per cent effective, which means that three to four per cent of those vaccinated can still get measles.

Generally, in Canada, kids are vaccinated at 12 months of age and then again between four and six years of age.

The measles vaccine contains a live, attenuated virus, “meaning you don’t want to give it to pregnant people,” said Dr. Caitlin Dunne, a reproductive specialist with the Pacific Centre for Reproductive Medicine in Vancouver. Women who are planning to get pregnant should wait a month, post-vaccination, before trying to conceive.

If a woman contracts measles during pregnancy, it can lead to birth complications like preterm birth and low birthweight infants, as well as serious pneumonia or respiratory illness in the mother, Dunne said.

When women are planning pregnancy, or are already pregnant, doctors check their blood for antibodies against rubella, or German measles, which can cause serious birth defects, such as brain abnormalities. “If someone is not properly immunized or immune to rubella, it may indicate as well that they’re also not immune to measles,” Dunne said, which could put the woman or her pregnancy at risk.

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“The best advice is to get your vaccines on schedule and if you’re not sure if you’ve been vaccinated, see your health-care provider. They may recommend a booster or a blood test to see your level of immunity, particularly if you are immunocompromised, a younger person or planning a pregnancy.”

What if I’ve been exposed to measles?

The vaccines were invented in the mid to late-60s; different provinces introduced the shots at different times. “After 1970, basically all provinces were rapidly introducing (measles vaccines),” said Ward, of McGill. “Because measles was so transmissible, the assumption we work on is that anybody born before 1970 was infected at one point in their lives,” and immunity after the disease is considered life-long.

Immunity after vaccination falls off very slowly, Ward said. “There are a small number of people who have had two doses of vaccination who will, at some point in their life, become susceptible again, probably not within 10 to 15 years of being vaccinated, but maybe 30 years after vaccination,” Ward said.

“But if the vast majority of people around you are vaccinated — and public health people put that number at around 95 per cent — then the chance of you being exposed is very, very small.”

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If people are travelling overseas to an area where measles is actively circulating, in most cases the recommendation is to get an extra dose of vaccine, Ward said. “If you don’t need it your body won’t even see it, and if you do need it, it’ll prevent you from getting a really bad disease while you’re overseas,” Ward said.

What if a child has had only one dose of vaccine and isn’t yet eligible for a second?

They still have pretty good protection against measles, Ward said. “If we start to see larger outbreaks, particularly in younger kids, I think what will happen is that provinces like Ontario that have that second dose at school entry will provide an extra dose earlier on.”

What should I do if I think I have measles?

If you or your child has a fever and rash, call your doctor or local public health unit right away. Call ahead so you can be seen quickly, and precautions taken to prevent infecting other people. Measles is diagnosed via a physical exam, blood test and throat swab or urine sample, according to HealthLinkBC.

People should stay home at least four days after the rash first appears, drink plenty of fluids (water, juice, soup, especially with fever) and get plenty of rest. Get emergency care if your child has a fever higher than 40.5 degrees Celsius, trouble breathing, confusion or clumsiness or a severe headache, according to John Hopkins Medicine.

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