What to know about NACI, blood clots and the AstraZeneca and J&J COVID-19 vaccines

By Mia Rabson, The Canadian Press

OTTAWA — With thousands of doses of Oxford-AstraZeneca vaccine creeping towards their expiration date in freezers across Canada, many provinces moved in mid-April to let people as young as 40 start getting vaccinated with them.

Generation X stepped up to get the first vaccine they were offered, but then the National Advisory Committee on Immunization came out with a warning: if you aren’t at particularly high risk of getting COVID-19, or getting really sick from it, then you might want to wait for the vaccines from Pfizer-BioNTech or Moderna instead.

Josh Greenberg, director of the school of journalism and communication at Carleton University in Ottawa, said the resulting confusion undermines the long-standing message to get the first vaccine you can.

“Lacking the expertise, the knowledge of the science, the quick decisions and interpretations people make is that this is a subpar substandard vaccine,” he said.

Here is what you should know about NACI, its latest advice and what it means for the vaccines produced by AstraZeneca and Johnson & Johnson.

What is the National Advisory Committee on Immunization?

The expert panel was created in 1964 to provide guidance on the use of new or existing vaccines in Canada. Its current 16 members include doctors, nurses and epidemiologists. They look at the current science behind a particular vaccine that has been authorized by Health Canada and come to a consensus on how the vaccine make the best impact.

In 2017, Health Canada authorized a new shingles vaccine. NACI did not issue its guidance until nearly a year later. They don’t have that kind of time during the COVID-19 pandemic and in some cases, the science is evolving constantly. New data that emerged on COVID-19 variants of concern was behind the sudden cancellation last month of a planned NACI briefing on AstraZeneca just minutes before it was to go live.

Is NACI part of Health Canada?

The advisory committee reports to the Infectious Disease Prevention and Control Branch at the Public Health Agency of Canada, but is considered an arm’s-length advisory body.

Its role is separate and distinct from Health Canada, which regulates the use of pharmaceuticals, reviews clinical data and determines if a particular drug can be used. NACI then provides guidance to the provinces on how it should be used.

That advice is not binding. Provincial governments, which have jurisdiction over health-care delivery, decide whether to follow it.

What did it actually say about the AstraZeneca and J&J vaccines?

NACI said that these vaccines potentially pose a risk of vaccine-induced thrombotic thrombocytopenia (VITT) — seven cases were seen in 1.7 million doses of AstraZeneca given in Canada, and 17 in eight million doses of J&J given in the United States.

The syndrome is similar to one caused by the blood-thinning drug Heparin, but has never been seen before with vaccines. It causes an immune response that affects the blood platelets leading to many small clots, which can be fatal if not properly treated.

Because VITT is potentially linked to the vaccines — it’s so new the link hasn’t yet been confirmed or the exact cause pinned down — NACI said the mRNA vaccines from Pfizer-BioNTech and Moderna that we know don’t cause the syndrome are “preferred.”

The AstraZeneca and J&J vaccines however are still effective against COVID-19, and for many people, the risks from COVID-19 far outweigh the risks of a blood clot.

How did NACI come to this conclusion?

NACI based its advice on a scientific, risk-benefit analysis that looks at the potential risk of dying from or ending up in the ICU with VITT — either one in 100,000, one in 250,000 or for J&J alone, one in 500,000. They compared those with how successful the vaccines would be at preventing an ICU admission or death from COVID-19.

The COVID-19 risks were further assessed based on five different community infection rates, from very low to very high.

They found, for example, that if VITT occurs at a rate of one in 250,000, the vaccines would prevent more deaths or ICU admissions across all age groups where infections rates were high or very high. That outweighed risk of a severe outcome from VITT.

The analysis ultimately found that because the risk of severe outcomes from COVID-19 for younger people are much lower, but the risk of the blood-clot disorder is the same across all age groups, then the AstraZeneca and J&J vaccines are more beneficial for older people who live in places with high COVID-19 infection rates.

What if you already got the AstraZeneca vaccine?

Dr. Shelley Deeks, NACI’s vice-chair, said the issue around the AstraZeneca and J&J vaccines is not about how well they protect anyone from COVID-19. It’s about the potential link to the rare blood-clotting disorder, which was not present in anyone who received the messenger RNA vaccines from Pfizer-BioNTech and Moderna.

She said the 1.7 million people in Canada who have already received the AstraZeneca vaccine should trust that they are protected.

“I would say to them that they have been offered an effective vaccine,” she said. “We’ve been very consistent in terms of our messaging through NACI that all COVID vaccines are safe and effective.”

She said once the risk period for VITT has passed, which NACI says is four to 20 days, then anyone who received AstraZeneca does not need to worry about blood clots at all.

This report by The Canadian Press was first published May 4, 2021.

Mia Rabson, The Canadian Press

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