Booster doses (third and fourth doses)
Protection after a primary series of the COVID-19 vaccine diminishes over time, particularly against the Omicron variant. COVID-19 vaccine booster doses help to boost protection against severe outcomes from the virus.
Dose numbers for booster doses may vary depending on a person’s primary series or specific circumstance (for example, people who received a COVID-19 vaccine outside of Canada). Most Ontarians received a two-dose primary series, so their first booster would be considered their third dose, and a second booster would be considered their fourth dose. If you are 18 and older, you can schedule your second booster appointment at a recommended period of five months (140 days), or a minimum period of three months (84 days) after your first booster. Ontarians aged 18-59 are recommended to speak with their health care provider about whether getting a second booster dose now is the right choice for them.
Individuals who are moderate to severely immunocompromised are able to get a three-dose primary series, so their first booster would be considered their fourth dose, and their second booster would be considered their fifth dose.
Three-dose primary series and boosters for individuals who are immunocompromised
Some individuals who are immunocompromised can get a third dose of the COVID-19 vaccine eight weeks after their second dose as part of an extended primary series. This includes eligible children aged five to 11 years old.
Eligible individuals aged:
- 12-17 years old can get a fourth dose (booster) six months (168 days) after completion of the three-dose primary series
- 18 years and older can get a fourth dose (booster) three months (84 days) after completion of the three-dose primary series
Contact your health care provider to see if you are eligible.
You might be eligible if you are:
- a transplant recipient (including solid organ transplant and hematopoietic stem cell transplants)
- receiving stable, active treatment (chemotherapy, targeted therapies, immunotherapy) for a malignant hematologic disorder or solid tumor
- in receipt of chimeric antigen receptor (CAR)-T-cell
- an individual with moderate or severe primary immunodeficiency (for example, DiGeorge syndrome, Wiskott-Aldrich syndrome)
- Stage 3 or advanced untreated HIV infection and those with acquired immunodeficiency syndrome
- undergoing active treatment with the following categories of immunosuppressive therapies: anti-B cell therapies (monoclonal antibodies targeting CD19, CD20, and CD22), high-dose systemic corticosteroids, alkylating agents, antimetabolites, or tumor necrosis factor (TNF) inhibitors and other biologic agents that are significantly immunosuppressive or are taking specific immunosuppressant medications(PDF)
- receiving dialysis (hemodialysis or peritoneal dialysis)
Appointments for a fourth dose (booster) can be booked through all vaccine channels.
Eligible individuals will need to provide their prescription, prescription vial, or a referral from a health care professional at the time of their appointment.
Where to get your vaccine
If you are eligible, you can book any of your vaccine doses:
- through the COVID-19 vaccination portal
- by calling the Provincial Vaccine Contact Centre at 1-833-943-3900
- directly through public health units that use their own booking system
- through Indigenous-led vaccination clinics
- participating pharmacies
- select primary care settings
- hospital clinics (visit your local hospital or public health unit for booking details, if available in your region)
- mobile or pop-up clinics, (visit your local public health unit website for details, if available in your region)
- GO-VAXX bus
- at your retirement home, long-term care home, elder care lodge, or congregate living setting (public health units will work with the homes to give you your shot within your home or at a mobile clinic)
If you book a vaccine through another channel, make sure to cancel your original appointment so that you do not take up a slot for someone else.