A recent increase in measles cases across Canada and internationally has people wondering why this once common childhood infection is making a comeback – and what to do about it.
In 1998, Canada achieved elimination status for measles thanks to widespread and successful routine vaccination programs. But public health officials are now warning about a significant increase in measles, due in part to a decrease in vaccinations during the pandemic.
Dr. Theresa Tam, Chief Public Health Officer at the Public Health Agency of Canada, says this trend combined with the upcoming spring break travel season is cause for concern.
“I am concerned that the global surge in measles activity, combined with the decline in measles vaccine coverage among school-aged children in Canada, could lead to an increase in imported measles cases, potentially resulting in transmission in communities in Canada,” Dr. Tam said in a statement on February 23, 2024.
“I strongly advise everyone in Canada to be vaccinated with two doses of a measles vaccine, especially before travelling.”
Dr. Jerome Leis is the Medical Director of Infection Prevention and Control at Sunnybrook Health Sciences Centre. He spoke to Your Health Matters about what people need to know about measles at this time.
What is measles?
Measles is a virus that is highly contagious but that fortunately is preventable as part of routine childhood vaccinations.
Before we had vaccines, measles used to cause large outbreaks with devastating complications. Since we started vaccinating for measles, it has almost disappeared. And yet we still see a resurgence of it from time to time, like when vaccine rates are slightly lower because even small differences in vaccine coverage can give measles an opportunity to transmit. It is the most infectious virus that we know.
Common measles symptoms include a respiratory infection with runny nose, inflamed and runny eyes, and a full body rash. These symptoms are generally mild. But measles can cause serious complications. The virus can lead to a bacterial infection like pneumonia. And sometimes the virus can travel to the brain and cause inflammation, called encephalitis, which can be very devastating especially for young children. This can lead to long-term morbidity due to the brain damage.
It is important to remember that these complications are completely preventable through vaccination. It is always unfortunate to see measles resurge when we know we can be doing better.
You said the measles virus is the most infectious virus we know. What makes it so contagious?
The virus has been recognized for a long time to be spread through the air. It can be inhaled in any air space where an infected person has been, often without being in close contact with the individual.
For example, you can be at a distance, you can be in an air space after the infected person has already left, and you can inhale those particles and become infected if you are susceptible. The rate of transmission for susceptible people is significantly higher than any other virus we know.
Why are we seeing more measles cases right now?
I think the major factor that we are seeing here is a pandemic related knock-on effect of the disruptions to primary care that occurred.
Keeping up to date with vaccines was less likely to occur during specific periods of the pandemic when children were not being seen for their regular vaccine appointments. There have been a lot of efforts to catch up on those missed vaccines, but when it comes to measles, even a one percentage drop in vaccine coverage introduces potential opportunity for measles to resurge.
In Europe, they have noticed a drop in vaccination rates and they have seen thousands of cases of measles in the last several months. In the Canadian context and in Ontario, what we are seeing is mostly cases of measles that are related to people who have travelled into those areas where there is more measles circulating.
The risk in Toronto is currently low but there are cases and even clusters of cases that are occurring, mainly following international travel. Most cases are related to people who are susceptible, meaning they have not had the two doses of vaccines required to provide optimal protection.
What is the MMR vaccine and how does it work?
The MMR vaccine is made up of attenuated viruses – meaning they are viruses that are not capable of causing infection but that will elicit a very strong immune response. In the MMR vaccine there are three attenuated viruses: measles, mumps, and rubella.
As part of the childhood vaccine series in Ontario, as in other provinces and territories across Canada, there are two doses of MMR that are given in childhood. And it is the two doses that give optimal long-term protection against measles.
The majority of measles cases we see, however, are people who have had less than two doses. Getting measles with two doses rarely occurs, but these breakthrough infections can happen. We generally see this when lots of measles is circulating, and these cases are usually milder.
It is clear that two doses of MMR is extremely effective against preventing these infections including measles. You can just look at how infrequent and rare measles has become since widespread vaccination with the two-dose schedule was introduced, as evidence. If vaccination rates decrease even a little, we experience outbreaks of measles.
Which groups are most vulnerable to measles?
Young children are particularly vulnerable to complications such as pneumonia and encephalitis, which can have devastating consequences.
Those complications are also more likely to happen in immune-compromised patients such as people who might have an underlying cancer or be receiving immune-suppressant treatment, or who have had an organ transplant. Those individuals may be susceptible and we cannot vaccinate them, so we need others to be vaccinated to protect them.
The other vulnerable group is pregnant people. Measles can cause pregnancy complications if the pregnant person becomes infected. We cannot give the vaccine to pregnant people because it is a live attenuated vaccine, so it is important to vaccinate people before they conceive.
Public health authorities are recommending people ensure they’re up to date on the MMR vaccine, especially if they’re travelling. What should people consider at this time?
If you are planning to travel, it is an opportunity to look at your vaccine record and make sure you are covered, especially if you are going to travel to higher risk areas.
If you have children who might have missed their usual vaccine appointments during the pandemic, or if you have recently come to Canada and might not have had the vaccine schedule that is in place here, or if you are planning to get pregnant in future, it is a good time to talk to your primary care practitioner to make sure you and your family are up to date on your vaccines and as protected as possible.
