Varicella (Chickenpox)

How Chickenpox Spreads

Chickenpox is caused by the varicella-zoster virus. It spreads through the air when an infected person breathes, coughs, sneezes or talks. People can become infected if they breathe the contaminated air or touch the infected surface, then touch their eyes, nose or mouth. The virus can also spread through contact with the fluid from chickenpox blisters (fluid-filled bumps).

Someone who has chickenpox can spread it to others starting one to two days before the rash appears until the last blister has scabbed over. Cases often increase during the school year and decrease over the summer.  

Symptoms & Illness

Symptoms usually start between 14 to 16 days after exposure but can start anywhere between 10 to 21 days after exposure.

Symptoms include:

• Fever
• Tiredness
• Cough
• Sore throat
• General aches and pains
• Itchy, red rashes appear and can spread to almost anywhere on the body. The rashes will gradually form into blisters and then scab over.

In healthy children, chickenpox can be relatively mild. However, complications can still happen including pneumonia (lung infection), blood and skin infections or swelling of the brain. An infection in pregnancy can cause congenital varicella syndrome and an infection in newborns can cause severe neonatal varicella. People with a weakened immune system can also get very ill.

After a chickenpox infection, many years later a painful rash can occur, called herpes zoster or shingles.

Varicella Vaccine

Vaccination against chickenpox is very safe and effective.

Children receive one dose of vaccine against varicella on its own, routinely at 15 months of age, then again as part of the measles, mumps, rubella, and varicella (MMRV) vaccine, which is routinely given at 4 to 6 years of age.

Varilrix®, VarivaxIII®

The varicella vaccine is very safe. The majority of reported side effects are mild, including fever, rash, and injection site reactions. The efficacy of varicella vaccines is estimated to be 94.4% following one dose, and 98.3% following two doses.

Varicella Vaccine Recommendations:

• Children aged 15 months should receive one dose of the univalent varicella vaccine as part of routine childhood immunizations.
• Children aged 12 months to under 13 years old who were not previously vaccinated in childhood should receive two doses of either MMRV or a univalent varicella vaccine.
• Adolescents (aged 13 to under 18 years old) and adults (aged 18 to under 50 years old) at risk of getting chickenpox should receive two doses of univalent varicella vaccine.

Learn more about MMR and MMRV Vaccines including the risks associated with vaccination against varicella, vaccination against varicella as part of the MMRV vaccine, people who should avoid or delay vaccination, and people who should be prioritized.

Seeking Medical Care & When to Isolate

If you or your child(ren) were in close contact with someone with chickenpox, watch for symptoms for 21 days after your last contact with that person.

If you think you or your child might have chickenpox: 

• Seek medical care right away. Call before visiting a clinic or hospital so they can prepare for your arrival and stop virus spread. 
• Stay home and away from others while you are sick to prevent spread.
• Wear a well-fitting, high-quality mask (e.g. surgical mask, N95) if you need to go out. 
• Wash or sanitize your hands often and cover your cough or sneeze with your elbow or a tissue. 
• Can return to child care settings or school as soon as you or your child are well enough to participate in normal activities, regardless of the state of the rash. 
• Health care workers with acute varicella illness must be excluded from work until lesions are dried and crusted. 

Diagnosis & Treatment

Health care providers generally diagnose chickenpox based on the characteristic rash, but if there is any doubt, a blood test, and a test using fluid from blisters, are available to confirm. This blood test can be used to find out if someone has chickenpox, recently had it, or is immune to the disease after an infection or vaccination.

In healthy children, chickenpox typically does not need to be treated, but medications may be prescribed to relieve itching or fever. The following are recommended to ease the symptoms of chickenpox at home:

• Avoid scratching rashes and blisters
• Use calamine lotion, or take a cool bath with added baking soda to relieve itching
• Eat soft, bland foods if blisters develop in the mouth

People at risk of complications may be prescribed antiviral medications to shorten the length of the infection to reduce their risk. If complications do occur, for example skin infections or pneumonia, antibiotics may be prescribed.

Talk to a health care provider to find out what treatment options might be available.

Chickenpox Exposure

If you are not immune to chickenpox, post-exposure immunization may be required depending on the level of exposure to chickenpox, your age and your immune system. Post-exposure management of healthy infants less than 12 months of age is not needed as these infants are generally protected by maternal antibodies. 

The following situations are considered significant exposures to a person who has chickenpox: 

• Living in the same home
• Being indoors with the infected person for more than 1 hour
• Being in the same hospital room for more than 1 hour, or more than 15 minutes of face-to-face contact
• Touching the blisters of the infected person, or clothing/personal belongings that may have touched their blisters

After being exposed, the chickenpox vaccine (not the MMRV vaccine) is generally provided to individuals who are not immune to the virus. For optimal effectiveness, it should be given within 72 hours after exposure and up to five days later. Varicella immune globulin may also be considered. 

Contact your health care provider for advice specific to your situation. 

Reporting Chickenpox to Toronto Public Health

Chickenpox needs to be reported to Toronto Public Health by schools, child care centres and health care providers.