Archive 22: Summary of National Advisory Committee on Immunization (NACI) statement: Recommendations on the use of COVID-19 vaccines

Publication date: October 22, 2021

On this page

• Overview
• What you need to know
  • Severe immediate allergic reactions (e.g., anaphylaxis) following vaccination with authorized COVID-19 vaccines
  • Optimal interval between the first and second doses of a two-dose primary COVID-19 vaccine series
• Quotes

Overview

• On October 22, 2021, the Public Health Agency of Canada (PHAC) released updated guidance from the National Advisory Committee on Immunization (NACI) on severe immediate allergic reactions after vaccination with COVID-19 vaccines, as well as updated information on the optimal interval between the first and second doses of a two-dose COVID-19 primary vaccine series. These recommendations are based on current scientific evidence and NACI's expert opinion.
• NACI has reviewed evidence from recent studies showing that most people who experienced immediate allergic reactions (e.g. anaphylaxis) after a first dose of an mRNA COVID-19 vaccine experienced no, or mild, reactions after a second dose of an mRNA COVID-19 vaccine.

NACI recommends that:

• People who experienced a severe immediate allergic reaction after a first dose of an mRNA COVID-19 vaccine can safely receive future doses of the same or another mRNA COVID-19 vaccine after consulting with an allergist or another appropriate physician. This group should also be observed for 30 minutes, instead of 15 minutes, after getting the vaccine.
• NACI has also reviewed emerging evidence on the ongoing positive impact of longer intervals between the first and second doses of a two-dose COVID-19 vaccine series. Data shows that extending authorized intervals by several weeks leads to even higher immune responses and better protection against COVID-19 infection that is also expected to last longer.

NACI has updated information on vaccine schedules:

• The interval between the first and second doses of a two-dose COVID-19 vaccine series that appears to be optimal are:
  • 8 weeks for the mRNA COVID-19 vaccines; and
  • At least 8 weeks for the AstraZeneca Vaxzevria COVID-19 vaccine.

To see the full update, please visit NACI Recommendations on the use of COVID-19 vaccines.

What you need to know

Severe immediate allergic reactions (e.g., anaphylaxis) following vaccination with authorized COVID-19 vaccines

• Very rare cases of severe immediate allergic reactions (e.g. anaphylaxis) after vaccination with authorized mRNA COVID-19 vaccines have been reported in Canada and internationally.
• Recent studies have shown that most people involved in those studies who experienced anaphylaxis after a first dose of an mRNA COVID-19 vaccine have been able to safely receive future doses of the same or another mRNA COVID-19 vaccine. In studies, the second dose was well tolerated with no or mild reactions.

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.
• People with a history of a severe immediate allergic reaction after a first dose of an mRNA COVID-19 vaccine should:
  • Consult with an allergist or another appropriate physician before receiving future doses of an mRNA COVID-19 vaccine;
  • Receive future doses of an mRNA COVID-19 vaccine in a controlled setting with someone who is experienced in managing anaphylaxis and
  • Be observed for at least 30 minutes after vaccination (the normal observation period for people who have not experienced a severe immediate allergic reaction after vaccination is 15 minutes).
• PHAC and Health Canada continue to closely monitor cases of anaphylaxis through Canadian surveillance systems and in collaboration with provincial and territorial health authorities, vaccine manufacturers and international regulators.
• People who have a confirmed severe immediate allergy to a component of a specific COVID-19 vaccine or its container (e.g., PEG) should consult with an allergist before receiving that vaccine.
• NACI continues to monitor the evolving evidence on severe immediate allergic reactions to COVID-19 vaccines and will update guidance as needed.

Optimal interval between the first and second doses of a two-dose primary COVID-19 vaccine series

• Most COVID-19 vaccines approved for use in Canada require two doses. The authorized intervals between the first and second doses were determined based on the interval chosen in initial clinical trials. The authorized intervals for two-dose COVID-19 vaccines approved in Canada are:
  • 3 weeks between doses for the Pfizer-BioNTech Comirnaty vaccine;
  • 4 weeks for the Moderna Spikevax vaccine; and
  • 4 to 12 weeks for the AstraZeneca Vaxzevria vaccine.
• Since the initial authorizations of COVID-19 vaccines, Canadian and international studies have been evaluating the impact longer intervals have on protection against COVID-19 disease.
• Data show that the very good protection provided by COVID-19 vaccines may be further improved when the interval between the first and second doses are extended beyond the authorized intervals. Emerging data shows that extending the interval by several weeks leads to higher immune responses and greater protection after the second dose.
• At this time, the intervals between the first and second doses of a two-dose COVID-19 vaccine series that appear to be optimal are:
  • 8 weeks for the mRNA COVID-19 vaccines; and
  • At least 8 weeks for the AstraZeneca Vaxzevria COVID-19 vaccine.
• When choosing to use a longer dose interval, local transmission of the SARS-CoV-2 virus; the degree of individual risk of exposure to the virus; and the need of a second dose for earlier protection should be considered.
• People who completed their primary vaccine series using manufacturer-authorized intervals also have very good protection against severe COVID-19 disease and do not need to restart their vaccine series.
• As with other vaccines, interruption of a vaccine series resulting in a greater than suggested interval between first and second doses does not require restarting the series since a delay between doses does not result in reduced protection after the second dose.
• It is important people continue to follow local recommendations regarding public health measures, especially while they wait for their second dose. The first dose provides some protection, but protection is increased following the second dose.
• The interval that provides optimal protection may change as more evidence is collected. NACI will continue to monitor the evidence and update information as needed.

To see the full update, please visit NACI Recommendations on the use of COVID-19 vaccines.

Quotes

"Canada took an approach early in the pandemic to get the most benefit from the COVID-19 vaccines available by extending the intervals between doses to maximize the number of Canadians benefiting from the first vaccine dose. This was supported by principles of vaccine science and early evidence on the performance of the vaccines. Over time, we have seen new evidence from Canada and the United Kingdom that suggest the strongest immune responses and protection may be achieved when the vaccine doses are provided at least 8 weeks apart. It is important to remember that these vaccines work very well in most people, and ensuring high vaccine coverage for the primary series is one of our most important tools in the pandemic response right now."

"NACI has been carefully monitoring the evolving evidence on anaphylaxis following COVID-19 vaccines. We are very encouraged to see that second doses can be safely provided even to those who have had a severe, immediate allergic reaction after a first dose of an mRNA COVID-19. This should be done with appropriate clinical oversight, and will help many more people have the very good protection against COVID-19 that can be achieved through a complete primary vaccine series."

"It is great news that NACI’s review of the latest evidence supports that people who experienced very rare immediate severe allergic reactions after receiving a first dose of a COVID-19 vaccine can safely receive subsequent doses of COVID-19 vaccines with appropriate clinical oversight. This means these individuals can receive the additional doses they need to complete their primary COVID-19 vaccines series and be better protected against COVID-19. "

"As well, updated information from NACI on optimal intervals between first and second doses of a COVID-19 primary vaccine series shows that extending intervals beyond initially authorized intervals leads to stronger immune responses, providing better protection against COVID-19 infection and severe outcomes. These updates are further examples of Canada’s ongoing commitment to carefully monitor vaccine safety, and to update vaccine advice as evidence evolves in order to provide Canadians with the best possible protection against COVID-19."