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Many adults I see in my practice have been asking me lately: With measles spreading across Canada, should I get a booster dose of the measles vaccine?
Here’s why measles is a growing concern right now and what you can do.
Why are people getting measles again?
Measles is a highly contagious, airborne disease that can result in serious health complications in some cases, including death.
Measles was eliminated in Canada in 1998, after the introduction of routine childhood immunization with a two-dose vaccine. The highly effective and safe measles-mumps-rubella (MMR) vaccine eliminated endemic transmission in Canada and created herd immunity in the population, which prevented further spread. However, the country is now seeing the largest measles outbreak in decades due to several factors, including a decline in routine childhood vaccination rates in some regions after the start of the COVID pandemic.
The Public Health Agency of Canada recently warned the country could lose its measles elimination status if the current chain of transmission continues beyond October.
Do you need a MMR booster?
If you are already fully vaccinated (i.e. you received both doses of the MMR vaccine) or have proven immunity to measles from a past infection, it is unlikely you will ever catch the virus and you do not need a booster.
You’re immune if one of the following applies to you:
- You received two documented doses of measles vaccine after one year of age, delivered at least 28 days apart
- You have serologic proof of immunity (i.e. a blood test that found antibodies to measles)
- You have had prior lab-confirmed measles
- You were born before 1970
Why people born before 1970 are considered immune
There was no measles vaccine prior to 1970. Given that measles is a highly contagious airborne virus, it can be safely assumed that everyone born before 1970 was exposed. If you survived this exposure, then you have already developed antibodies and are considered immune.
In this case, you do not need another shot of measles vaccine – unless you are in one of the groups Health Canada’s Immunization Guide lists as susceptible, such as health care workers.
What to know if you were born after 1970
If you were born after 1970, check your measles vaccination records, if possible, to see if you received two doses of the MMR vaccine. Protection is estimated to be 85 to 95 per cent if you’ve had one shot in your lifetime, and nearly 100 per cent if you’ve had two shots. Some people may need a second shot to boost their measles protection to near complete levels.
If you fall into this age group but don’t have your vaccination records and – importantly – if you have a healthy immune system, there is no harm to getting a dose of the MMR vaccine, which has a decades-long history of proven safety and efficacy for immune competent individuals. Sometimes getting another shot is easier than getting a bloodwork requisition to check for measles immunity.
However, a minority of people should not get the MMR vaccine. For example, if you have an immune compromising condition or are on immunosuppressant drugs, or if you are pregnant, you may not be able to get an MMR vaccine. For some immunocompromised individuals, other treatments may be given to prevent against measles. Consult with your primary care provider to find out what the recommendations are in your specific case.
What if I’m planning to travel to one of the outbreak zones?
The same advice applies: You do not need a booster if you are already immune to measles.
However, if you are pregnant or immune compromised and thus at higher risk for serious outcomes of infection and not able to receive a dose of MMR vaccine, consider deferring travel or reaching out to your doctor for specific travel advice.
If you will be travelling to one of the outbreak areas with an infant under one year old, it’s worth noting that infants are able to get an early dose as young as six months old. Babies who receive a shot before they turn one would still need two more shots to be fully protected against measles.
Dr. Yan Yu is a family physician in Alberta and the Northwest Territories and the founder and director of Joyce Health, an online child and adolescent psychiatry clinic. He works in a wide range of clinical settings, including in rural and remote communities and creates medical education videos in his spare time.
