COVID-19 vaccine update: Fourth doses for additional populations (second booster) and Moderna primary series for 6 to11 year olds with moderate to severe immunocompromise

Advisory Alert

April 7, 2022

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To: Local Health System Partners


This Advisory Alert provides an overview of the updated Ministry of Health COVID-19 Vaccine Third Dose and Booster Recommendations (PDF, 300 KB) following the provincial announcement ( issued Wednesday, April 6, 2022. Specifically, highlighted within is information on population groups newly eligible and strongly encouraged to receive a fourth dose (second booster) of the COVID-19 vaccine, in addition to those groups already eligible. Further, included is new Moderna eligibility for the three-dose primary series for those 6 to 11 years of age who are moderately to severely immunocompromised.

Expanded eligibility for fourth dose booster of COVID-19 vaccine

The Ontario Government is expanding eligibility for fourth doses to provide an extra layer of protection against both the Omicron BA.1 and BA. 2 variants. Starting April 7, 2022, fourth-dose eligible populations will include:

The Government of Ontario (PDF, 300 KB) recommends that these individuals receive their fourth dose (second booster) five months (140 days) after they received their third dose (first booster). With informed consent the fourth dose (second booster) can be received 3 months (84 days) after their third dose (first booster). Those individuals who have acquired COVID-19 since receiving their third dose (first booster) should wait at least three months before receiving their fourth dose (second booster).

The COVID-19 vaccines remain one of our best defences against COVID-19 and its variants. Eligible individuals are strongly encouraged to receive a fourth dose (second booster) as soon as they are eligible to enhance their immunity and have better protection against severe illness and hospitalisation.

Continued eligibility for fourth doses of COVID-19 vaccine

Fourth doses continue to be offered to and are strongly recommended for select populations who became eligible in January 2021. These populations include:

NEW: Moderna use in 3-dose primary series for moderately to severely immunocompromised children 6-11 years old

Moderately to severely immunocompromised individuals aged 5 to 11 years are recommended to receive a three-dose primary series. Eligible individuals aged 5 to 11 years should be given the pediatric Pfizer-BioNTech Comirnaty (10 mcg). However, consideration for use of the Moderna Spikevax (50 mcg) vaccine may be provided for moderately to severely immunocompromised individuals ages 6 to11 years. Indirect data from adult populations suggests Moderna Spikevax (100 mcg) may result in higher vaccine effectiveness and is associated with a higher seroconversion rate among adult immunocompromised patients. Given the potential benefit, administration of the Moderna Spikevax (50 mcg) vaccine as a 3-dose primary series in this population is outlined in the product monograph (PDF, 458 KB).

Please be advised that immunocompromised individuals wanting to receive a fourth dose must have proof of an eligible prescription or a completed third or fourth dose referral form (PDF, 132 KB) when they arrive at the clinic. For more information on fourth dose eligibility in these populations review the Ministry of Health’s Third Dose Recommendations (PDF, 300 KB) and the Advisory Alert published January 14, 2021.

Primary care providers interested in offering the COVID-19 vaccine through their practice are asked to contact us at To request additional COVID-19 vaccines please contact us at Primary care has multiple roles to play in the vaccine program including onboarding practices to administer the vaccine in their offices, supporting vaccination clinics, and ongoing patient education on vaccine safety and efficacy.

Local vaccination opportunities

Visit our Vaccination clinics for COVID-19 webpage for information on clinic dates, times, and locations. Eligible clients can attend a walk-in vaccination clinic or book an appointment online at or by calling 705.674.2299 (toll‑free: 1.800.708.2505), between 8 a.m. and 6 p.m., Monday to Friday. Clients can also contact a local participating pharmacy, primary care provider, or health centre.


Original Signed By

Dr. Penny Sutcliffe
Medical Officer of Health and Chief Executive Officer

NOTE: All Advisory Alerts are found on our website.

This item was last modified on April 8, 2022