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NACI Offers New Advice For 2nd AstraZeneca Shots

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A key federal advisory committee is no longer recommending that Canadians receive a second dose of the AstraZeneca vaccine.

The National Advisory Committee on Immunization (NACI) previously said that people who received a first dose of AstraZeneca could get it as their second or could choose an mRNA vaccine, such as Pfizer or Moderna.

But new guidance released Thursday said the Pfizer or Moderna vaccine is “now preferred” for the second dose.

“This change is based on emerging evidence indicating a potentially better immune response from this mixed vaccine schedule and to mitigate the potential risk of VITT associated with viral vector vaccines,” Dr. Theresa Tam, Canada’s chief public health officer, said in a news conference.

VITT is a rare blood clot that has occurred in some people who received the AstraZeneca shot.

NACI also recommended that an mRNA vaccine is preferred as a first dose unless one is inaccessible or there is a contraindication, for example, an allergy to an mRNA vaccine or its components.

“I wish to emphasize that people who received two doses of the AstraZeneca/COVISHIELD vaccine can rest assured that the vaccine they received provides good protection against infection and very good protection against severe disease and hospitalization,” said Tam.

NACI is now also recommending that people who received Pfizer or Moderna as their first dose should be offered the same vaccine for their second.

Tam said if the same vaccine is not readily available, the mRNA vaccines are considered “interchangeable,” meaning a person can be offered another mRNA vaccine instead.

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Canadians Can Safely Mix COVID-19 Vaccines: NACI

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Canada’s National Advisory Committee on Immunizations says it’s safe for Canadians to mix COVID-19 vaccine types.

Dr. Theresa Tam, Canada’s Chief Public Health Officer, announced Tuesday anyone with their first dose of AstraZeneca can receive an mRNA vaccine like Pfizer-BioNTech or Moderna, for their second dose.

Those who received a first dose of a mRNA vaccine are advised to get a second dose of the same type, but if they are unavailable when it comes time for the second shot Tam said Pfizer and Moderna can be ‘considered interchangeable.’

“The interchangeability of vaccines means you can receive one vaccine product for your first dose, and safely receive a different vaccine for your second dose to complete your two-dose vaccine series for optimal protection from COVID-19,” Tam said.

As provinces reach the threshold of offering first doses to all Canadians aged 12 and older, Tam says it’s now important to turn our attention toward getting second doses into the arms of the most vulnerable residents.

“The committee recommended last week that second doses be offered as soon as possible. NACI recommends that priority for second doses should be given to those at highest risk of severe illness and death from COVID-19 disease after or at the same time as first doses are offered to all remaining eligible populations,” Tam said in a press briefing.

The announcement follows studies and clinical trials into vaccine interchangeability in Germany, Spain and the United Kingdom.

Updated guidance from NACI says those studies show following a dose of AstraZeneca with a mRNA vaccine provides an immune response boost, though there is a possibility of increased short-term side effects, including headache, fatigue and general illness.

Studies have also shown that while the risk of VITT or blood clots caused by vaccines appears to be lower from a second dose, the rate has increased over time. NACI says the second dose of AstraZeneca appears to trigger VITT in 1 out of every 600,000 people who received the shot.

NACI also says so long as Canadians receive two doses of any of the three currently-approved COVID-19 vaccines that individual should be considered to be fully vaccinated from COVID-19.

Individual provincial governments will now have to consider NACI’s guidance and determine whether they will offer residents the opportunity to mix vaccine types for their second doses.