MEDICAL ADVISORY: COVID-19 Booster Doses After Completing A Primary Series
Issued by: M. Mustafa Hirji, MD, MPH, FRCPC, Medical Officer of Health & Commissioner (Acting)
On October 29, 2021, the National Advisory Committee on Immunization (NACI) released interim guidance on booster COVID-19 vaccine doses in Canada.
According to NACI, there continues to be no evidence of population-wide waning of immunity against severe illness. Lower vaccine effectiveness against severe disease has mainly been identified in residents in long-term care homes, with some evidence of decreased effectiveness in elderly adults, particularly those 80 years of age and over.
Emerging evidence suggests vaccine effectiveness against asymptomatic infection and mild COVID-19 disease may decrease over time, however, the short interval (3-5 weeks) between doses and the emergence of variants may be the true
contributors to observed lower effectiveness.
Where there has been waning of infection in elderly persons, studies suggest that a booster dose of an mRNA COVID-19 vaccine produces a very good immune response that is generally higher than the immune response after the primary series, has a favourable safety profile, and provides good short-term protection against infection. It is currently unknown how long effectiveness from a booster dose may last.
Ontario Plan for Booster Doses
On November 3, the province
announced that they are expanding eligibility for booster doses based on evidence of gradual waning immunity in elderly persons six months after receiving their second dose, and a higher risk of severe illness from COVID-19 for these populations. The following individuals will be eligible for booster doses of the COVID-19 vaccine at least six months after their last dose
- Individuals aged 70 and over (born in 1951 or earlier);
- Health care workers and designated essential caregivers in congregate settings. Refer to Appendix B (page 16) from the Ministry of Health COVID-19 Vaccine Third Dose Recommendations guidance document for a list of health care workers eligible for booster doses.
- Individuals who received a complete series of a viral vector vaccine (two doses of the AstraZeneca vaccine or one dose of the Janssen vaccine); and
- First Nation, Inuit and Métis adults and their non-Indigenous household members who are 18 years of age and older
- At this time, Ontario is not actively recommending third or booster doses for First Nation, Inuit and Métis
individuals under 18
There is no change to the eligibility for a third dose for previously announced groups. Please refer to the Ministry of Health COVID-19 Vaccine Third Dose Recommendations guidance document for full eligibility details.
The province also indicated that in early 2022, they may expand eligibility for booster doses based on age and risk, with an interval of six to eight months from the second dose.
Process for Vaccinating Eligible Individual with Booster Doses
- Newly eligible individuals are able to book their booster dose appointment through the Provincial COVID-19 vaccination portal or by calling the Provincial Vaccine Contact Centre at 1-833-943-3900
- Niagara Region Public Health strongly recommends clients make a booked appointment for their booster dose to avoid long waits and to ensure vaccine availability
- Eligible individuals will also be able to receive a booster dose at participating pharmacies
- Health care provider offices administering the COVID-19 vaccine may also provide booster doses to their eligible patients
Recommendations on Vaccine Product and Dosage for Third or Booster Dose
- Either mRNA vaccine may be used as a third or booster dose
(regardless of which COVID-19 vaccine was used in the primary series). If offering
- Pfizer-BioNTech’s Comirnaty vaccine for a third or booster dose
- The full dose (30 mcg) is recommended
- Moderna’s Spikevax vaccine for a third or booster dose
- A full dose (100 mcg) is recommended for residents of long-term care homes,
retirement homes or seniors in other congregate living settings, adults 70 years of age and older, and all eligible immunocompromised individuals
- A half dose (50 mcg) is recommended to anyone else less than 70 years of age
- Individuals that received AstraZeneca/COVISHIELD for their first and second dose are recommended to receive an mRNA vaccine for their third or booster dose unless contraindicated. A booster dose of a viral vector vaccine should only be considered when an mRNA vaccine is contraindicated or inaccessible.
- NACI recommends that it is possible for people who experienced a severe immediate allergic reaction after a first dose of an mRNA COVID-19 vaccine to safely receive future doses of the same or another mRNA COVID-19 vaccine in a controlled setting after consulting with an allergist or another appropriate physician. These individuals should also be observed for at least 30 minutes after vaccination.
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