^{Shelly Bolotin (left) and Sarah Wilson}

June 24, 2024

By Betty Zou and Ishani Nath

With measles cases in Canada reaching historic highs, public health officials are urging parents to ensure children are up to date on their measles vaccinations — especially for those planning summer trips.

Measles is one of the most contagious infectious diseases and can cause serious health complications including blindness, brain swelling, pneumonia and death.

“We’re a very globally connected world, so when there’s measles anywhere, there’s a risk of measles everywhere,” says Shelly Bolotin, Director of the Centre for Vaccine Preventable Diseases (CVPD) and a member of the Emerging and Pandemic Infections Consortium (EPIC). “That means if measles is elsewhere in the world, it’s coming to Canada… so it’s very important that we stay on track and catch up any kids that missed vaccinations during the pandemic.”

Typically, children in Canada receive a measles vaccine around their first birthday and a second dose either at 18 months or between ages four and six, depending on where they live. But with the recent increase of measles cases in Canada and around the globe, plus the summer travel season, some parents are wondering whether they should stick to the immunization schedule or get their children vaccinated now.

We spoke with Bolotin and public health physician Sarah Wilson, who is also a member of the CVPD, to learn more.

Why do children need two doses of the measles vaccine to be protected against measles? 

Measles-containing vaccines, whether it is MMR (measles, mumps and rubella) or MMRV (measles, mumps, rubella and varicella), are very safe and effective vaccines for protecting against measles.

Even one dose of a measles vaccine provides protection against measles, explains Wilson. According to the Canadian Immunization Guide, a single dose of  measles vaccine given at 12 months or 15 months is between 85 and 95 per cent effective at protecting against measles.

While this effectiveness is high, Bolotin explains that a small number of individuals “don’t make an adequate immune response” after their first dose, meaning they could still contract or get really sick from measles. That’s why a second dose is recommended. After a second dose, the Canadian Immunization Guide states that measles vaccines are “almost 100 per cent” effective.

Simply put, Wilson says, “One dose of measles vaccine is very good, but two doses are even better.”

When should parents consider getting their child vaccinated for measles early? 

Travel is the main reason to consider giving a child a measles vaccine early.

“The majority of the measles cases diagnosed in Ontario in 2024 have occurred in people with a history of travel outside of Canada,” says Wilson. She adds that all children who are one year or older are recommended to get two doses of the measles vaccine before traveling outside of Canada, even if their second dose is ‘early.’

Beyond that, measles immunizations are important for travelers of any age. “The vast majority of cases have occurred in individuals who are either unimmunized or who don’t know their measles immunization status and as a result their immunization status is described as unknown. These figures are a reminder that all family members should ensure they are protected against measles before travelling, not just children.”

Another situation where it might be recommended that a child get vaccinated early is if they have been exposed to measles to reduce the risk of developing measles or reduce the severity if they get infected, says Wilson. “An early dose might also be recommended by public health if a local measles outbreak were ever declared.”

Are there risks to getting measles vaccines early? 

The short answer is no.

The age when children get their measles vaccines in Canada is determined by a mix of considerations like how long babies are protected by their mother’s antibodies and the historically low risk of being exposed to measles in Canada, explains Wilson. But in countries where measles is more prevalent, children get vaccinated at younger ages.

“Although an immune response is better at 12 months, it’s definitely worth vaccinating a baby early — as early as six months — if the risk of measles is increased, like if they’re traveling abroad,” says Bolotin.

Does getting the first dose of the measles vaccine before age one reduce its effectiveness? 

“We put a lot of thought into the age at which we administer the first dose, there are several things that we’re trying to balance out,” says Bolotin. With measles vaccines, that includes a child’s risk of getting measles and their maturing immune system.

“It takes several months and even into the second year of life to fully mature from an immunological basis,” Bolotin explains. “So we expect a better immune response if we wait until the 12-month mark to vaccinate, making the vaccine a little bit more effective than if we administer the vaccine a little bit earlier at six months.”

That said, there are factors to consider, such as travel. Wilson explains it is recommended that children who receive an early dose (i.e. before their first birthday), get an additional two doses.

If my child gets their first dose early, does that change when they should get their second dose and whether they need a third?

“If a child is immunized with their first dose of measles containing vaccine at earlier than 12 months, that is what we call a zero dose,” says Bolotin. “It is very, very helpful when infants are traveling out of the country to measles endemic areas. However, it does not count as our first dose of measles vaccine for immunization for school.”

So, children who receive a measles vaccine early, say at nine or 10 months, due to travel, are still recommended to get a dose on or after their first birthday (as long as it’s been 28 days since their last measles vaccine) and then another dose either at 18 months or between the ages of four and six years, depending on their provincial immunization schedule. “The reason for these additional doses given on and after the first birthday is to ensure long lasting protection to measles that will protect the child into adulthood,” says Wilson.

Additional resources:

The measles, mumps and rubella (MMR) vaccine: What you need to know (Immunize Canada)

Global Measles Notice (Government of Canada)