Measles: Spread, prevention and risks
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How measles spreads
Measles is a viral infection that can easily spread to people who aren't immune. To be immune, you must have been vaccinated or previously infected with measles.
The measles virus can live up to 2 hours in the air or on surfaces in a space where someone with measles has been.
You can become infected with the measles virus when you:
- breathe in air containing infectious respiratory particles, such as in a location where someone who's infected with measles is or has recently been
- have direct contact with secretions (for example, saliva or mucus) from the nose or throat of someone who's infected
- touch a contaminated surface or object and then touch your eyes, nose or mouth before cleaning your hands
If you're infected, you can spread measles to other people from 4 days before until 4 days after the rash appears. If you don't develop a rash, you can still spread measles up to 10 days after the initial symptoms appear.
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Preventing measles with vaccination
There are 2 kinds of measles-containing vaccines in Canada, and both also offer protection against other infections. They are the:
- measles-mumps-rubella (MMR) vaccine
- measles-mumps-rubella-varicella (MMRV) vaccine
- varicella is also called chickenpox
The first dose of a measles-containing vaccine is usually given to children at 12 months of age.
The second dose of a measles-containing vaccine is usually given to children at 18 months of age or 4 to 6 years of age.
One dose of a measles-containing vaccine given after 12 months of age is up to 95% effective at preventing measles. Having 2 doses is about 99% effective.
Vaccination schedules vary depending on your province or territory.
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Adults born before 1970
If you were born before 1970, you're presumed to have immunity as it's likely you were infected with the measles virus when you were younger. However, a measles-containing vaccine may be recommended if you are:
- a health care provider
- travelling internationally
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Adults born in or after 1970
Adults born in or after 1970 are recommended to receive at least 1 dose of a measles-containing vaccine.
Additionally, for adults born in or after 1970, 2 doses of a measles-containing vaccine are recommended if you are:
- a health care worker
- travelling internationally
- attending post-secondary education, such as college or university
Talk to a health care provider to make sure you have had all the measles-containing vaccine doses recommended for you.
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People who are pregnant or immunocompromised
People who are pregnant or immunocompromised (have a weakened immune system) are generally not recommended to receive a measles-containing vaccine. However, they should consult with a health care provider if they're not previously vaccinated and are at risk of exposure to measles.
Safety of measles-containing vaccines
After vaccination, it's common to have mild temporary side effects at the site where the vaccine was given, including swelling, soreness and redness.
Within 1 to 3 weeks after vaccination, some people may develop 1 or more of the following:
- fever
- mild rash
- temporary joint pain or stiffness
- swelling of the neck lymph nodes
- swelling of the glands of the cheeks
These side effects are expected and usually go away within a few days. You can take medication if needed for pain or fever. Check with a health care provider if you have any concerns or need advice about which medication to use.
Very rarely, someone may have a serious reaction to a vaccine, including an allergic reaction. Symptoms of a serious allergic reaction typically happen soon after vaccination and can include:
- breathing problems (wheezing)
- swelling of the face, tongue, lips or throat
- red bumps on the skin that are often itchy (hives)
If you suspect you might be having a serious allergic reaction after a vaccination, seek medical care right away.
Serious allergic reactions and side effects from vaccines should also be reported to your local public health unit or office.
Tell a health care provider about any serious allergic reactions or side effects you've experienced before you receive future vaccinations.
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If you've been exposed
If you think you've been exposed to measles, contact a health care provider or your local public health unit or office right away. They will do an assessment and determine if you:
- are at risk of serious complications and
- should receive a measles vaccine or protective antibodies (immunoglobulin)
This is called post-exposure prophylaxis. It should be given as soon as possible after exposure to help prevent or reduce the severity of a measles infection.
You should also monitor yourself for symptoms of measles for at least 21 days after you were exposed. During this time, the public health unit or office may also recommend that you avoid certain higher-risk settings and use public health measures. These actions will help reduce the risk of potentially infecting others. This may include wearing a respirator or mask.
If you do develop symptoms during your self-monitoring period, you should:
- isolate away from others immediately
- contact your health care provider or the local public health unit or office for advice
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Who is most at risk
Canada generally has high vaccination rates against measles, which helps prevent the virus from spreading. However, there are some communities and regions where vaccination rates are low. You're at higher risk of measles exposure if you live in or travel to an area where measles is circulating.
Measles cases and outbreaks still happen in Canada, as measles is present worldwide and travellers who aren't immunized can bring measles into Canada.
You're more likely to become infected if you:
- haven't previously been vaccinated or had a measles infection and
- are travelling to or residing in regions where measles is circulating
Some people are at higher risk of developing severe complications from measles, including:
- infants and children under 5 years of age
- people with weakened immune systems
- people who are pregnant
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