A booster dose of COVID-19 vaccine is an additional shot of vaccine that helps maintain and lengthen individual’s protection against severe outcomes of COVID-19. Booster dose is believed to protect individual and the people around from COVID-19. Studies show after getting vaccinated against COVID-19, protection against the virus and the ability to prevent infection with variants may decrease over time and due to changes in variants. The recent emergence of the Omicron variant further emphasizes the importance of vaccination, boosters, and prevention efforts needed to protect against COVID-19.
Clinical trials have shown that a COVID-19 booster dose increases the immune response in people who have completed a COVID-19 vaccine primary series 6 months earlier or who have received a Johnson & Johnson’s Janssen COVID-19 single-dose vaccine 2 months earlier. With an increased immune response, people should have improved protection against getting infected with COVID-19. A booster shot is for the people who may built enough protection after completing their primary vaccine series, but afterwards that protection decreased over time. Hence, it is recommended by health authorities that everyone ages 12 years and older who has completed their primary series should get a booster.
Canada’s National Advisory Committee on Immunization (NACI) has released guidance on booster COVID-19 vaccine doses in Canada. The chief objectives are :
a. To minimize serious illness and death,
b. To preserve health care capacity, and
c. Reduce transmission to protect high risk populations.
d. Booster doses of COVID-19 vaccines can increase the immune response and offer more protection against infection.
The intent of a booster dose is to increase protection that may have decreased over time. Individuals with two valid doses will still be considered fully vaccinated. Booster doses are highly recommended as they can help protect the most vulnerable members of our region and our essential healthcare workers. Although COVID-19 vaccines remain effective in preventing severe disease, recent data suggest their effectiveness at preventing infection or severe illness wanes over time, especially in people ages 65 years and older.
Data from clinical trials have shown that a booster shot increased the immune response in trial participants who completed a Pfizer-BioNTech or Moderna primary series 6 months earlier or who received a Johnson & Johnson’s Janssen COVID-19 single-dose vaccine 2 months earlier. With an increased immune response, people should have improved protection against getting infected with COVID-19. For Pfizer-BioNTech and a Johnson & Johnson’s Janssen, clinical trials also showed that a booster shot helped prevent severe disease.
Eligible groups for third doses/ booster dose of the COVID-19 vaccine
Adults 18 years of age and older - who have received a primary COVID-19 vaccine series are strongly recommended to get a booster dose of an mRNA COVID-19 vaccine (Pfizer Comirnaty® or Moderna Spikevax®) at least 5 1/2 months after the administration of the second dose
The following groups are at highest risk for hospitalization and are strongly recommended to get a booster dose at 5 1/2 months after the administration of the last dose of vaccine:
Adults aged 50 and older
Health care workers with direct in-person patient contact (regardless of the interval between the 1st and 2nd doses);
Residents of long-term care and community care facilities 18 years of age and older
Those who are moderately to severely immunocompromised (after the primary series of three doses)
Individuals 18 years of age and older who received two doses of the AstraZeneca Vaxeveria™ vaccine or one dose of the Janssen vaccine
Other eligible groups for third dose/booster dose include:
Anyone who has received one or two doses of a non-Health Canada authorized vaccine (e.g. Covaxin, Sinovac or Sinopharm) to optimally protect against COVID-19.
Individuals who need to travel internationally for essential reasons and received a mixed dose of COVID-19 vaccines can get a matching dose of mRNA vaccine
For essential international travel - Some international countries are not recognizing people as being fully vaccinated if they have received a mixture of COVID-19 vaccines.
Various COVID vaccines and immunity
It typically takes a few weeks after vaccination for the body to produce T-lymphocytes and B-lymphocytes. Different types of vaccines work in different ways to offer body immunity or protection. However, with all types of vaccines, the body receives a supply of “memory” T-lymphocytes as well as B-lymphocytes that remember how to fight that virus in the future. Since it takes some time after the vaccination for the body to produce lymphocytes for immunity purpose, it is possible that a person could be infected with the virus that causes COVID-19 just before or just after vaccination and then get sick because the vaccine did not have enough time to provide protection.
Fully vaccinated and a booster dose
In Ontario, an individual is considered fully vaccinated if they have received:
The full series of a COVID-19 vaccine authorized by Health Canada or any combination of such vaccines,
One or two doses of a COVID-19 vaccine not authorized by Health Canada, followed by one dose of a COVID-19 mRNA vaccine authorized by Health Canada, or
Three doses of a COVID-19 vaccine not authorized by Health Canada; and
They have received their final dose of the COVID-19 vaccine at least 14 days ago.
COVID Infection, immunity & vaccination
Even if one has already had COVID-19 and recovered, one should still get their booster dose. While some increase in immunity after being infected with COVID-19 may be experienced, it is not enough to increase the overall immunity over a longer period of time. As per Health authority guidelines, getting a booster dose, even after having COVID-19, will provide increased and longer-lasting protection to reduce future infection, community transmission and severe illness.
Those who were recently infected, can get their booster dose 3 months after they have first experienced symptoms of COVID-19 or since the date of their positive test (and it must be at least 5 ½ months since the second dose before they are eligible for their booster dose).
Vaccines effectivity at preventing the spread of the Omicron variant
As such, currently, the data remains limited to establish the complete vaccine effectivity at preventing the spread. However, as per the recent statement by the Canadian Council of Chief Medical Officers of Health, there is emerging evidence that two doses of a mRNA vaccine are less effective at preventing Omicron infection compared to previous variants but does indicate good protection against more severe disease requiring hospitalization.
A booster dose is believed to be a valuable tool to offer protection from infection and it is expected that a booster dose will offer very good protection against severe disease. Not sufficient data are available at this moment to exactly confirm how long the protection from boosters will last, nonetheless, booster dose is believed to be an important tool at this time to help protect our collective progress against COVID-19 and preserve health care system capacity. As per NACI, emerging evidence indicates that a longer interval between SARS-CoV-2 infection and vaccination is associated with improved antibody responses to COVID-19 vaccines.
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