NACI recommends mRNA second jab for first-dose AstraZeneca recipients 

The National Advisory Committee on Immunization (NACI) has updated its guidelines to recommend that those who received AstraZeneca for their first dose should get an mRNA vaccine as a second jab.

In a statement issued yesterday NACI Chair Dr. Shelley Deeks said: “With mRNA vaccine supply in Canada continuing to increase and the ongoing risk of the rare but serious adverse event called VITT (Vaccine-Induced Immune Thrombotic Thrombocytopenia/blood clots)  that is associated with the viral vector vaccines after first and second doses, NACI now recommends that an mRNA vaccine is the preferred choice for starting a COVID-19 vaccine series.

“NACI is also recommending that for anyone who received a first dose of AstraZeneca/COVISHIELD, an mRNA vaccine is now preferred for the second dose. Since NACI first looked at mixed vaccine schedules, new evidence is starting to emerge suggesting immune responses are better when a first dose of the AstraZeneca vaccine is followed by an mRNA vaccine as a second dose. NACI understands individuals may feel uncomfortable following a mixed vaccine schedule and suggests speaking with a healthcare professional about the decision on which vaccine product to receive for their second dose,”  added Deeks

The rate of VITT after the second dose of the AstraZeneca/COVISHIELD vaccine appears to be lower than with the first dose but has increased over time, with current estimates of approximately 1 per 600,000 people vaccinated, NACI pointed out while reiterating that individuals should to talk to a healthcare professional about the best option for their situation.

However, the advisory body also reassured Canadians who have already received two doses of AstraZeneca/COVISHIELD that the vaccine provides good protection against infection and very good protection against severe disease and hospitalization. 

“Anyone who has already received two doses of AstraZeneca/COVISHIELD can rest assured that they are protected, particularly against severe illness. There is no need for a third dose at this time,” said Deeks.

NACI has come under fire for its contradictory advice, which some healthcare professionals believe could promote vaccine hesitancy.

The advisory committee had initially recommended that people who wanted earlier vaccination could receive a viral vector vaccine (AstraZeneca/COVISHIELD, Janssen) rather than wait for an mRNA vaccine (Pfizer-BioNTech, Moderna) if certain conditions were met. 

It later revised its stance to say that that an mRNA vaccine is preferred as a first dose and viral vector vaccine may be offered to individuals in the authorized age group when an mRNA vaccine is inaccessible or contraindicated, for example because of an allergy to an mRNA vaccine or its components.

NACI has defended this advice saying that the first guidelines “reflected the limited supply of mRNA vaccines at the time and the imperative of protecting vulnerable populations from serious illness and death from COVID-19”. The recommendation was “based on a public health benefit-risk analysis comparing the rates of VITT and the risk of COVID-19 while waiting for an mRNA vaccine”, NACI said in a statement.

Meanwhile NACI is recommending that individuals who received a first dose of an mRNA vaccine (Pfizer-BioNTech, Moderna) should be offered the same mRNA product for their second dose. If the same product is not readily available, or the product used for the first dose is unknown, another mRNA vaccine is considered interchangeable and should be used to complete the series.

“NACI’s independent guidance on the use of authorized COVID-19 vaccines is invaluable to Canada’s pandemic response,” said Canada’s Chief Public Health Officer Dr. Theresa Tam. The evolution of its recommendations, based on rapidly emerging scientific evidence, provides public health authorities with sound advice to help protect the health and well-being of Canadians. Because of the international research effort, we are learning more about COVID-19 every day.”

“The experts on NACI are continuously analyzing complex data and scientific information and applying their expertise to guide us in the optimal use of COVID-19 vaccines,” Tam added.



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