The National Advisory Committee on Immunization adjusted Tuesday its advice for the use of the Oxford-AstraZeneca vaccine to say that it can now be given to seniors.

On March 1, NACI said the vaccine was not recommended for use on people 65 years of age and older because there were not enough people in that age group included when AstraZeneca conducted its clinical trials.

It recommended the Pfizer-BioNTech and Moderna vaccines be prioritized for seniors, and AstraZeneca given to younger populations who might otherwise wait longer to get a vaccine.

Here are five things to know about Tuesday's decision and NACI:

1. What did NACI specifically say about the vaccine and seniors?

NACI said there are two studies from the United Kingdom which looked at how effective AstraZeneca was against COVID-19.

The studies found signs of significant effectiveness against symptomatic COVID-19, and reduced hospitalizations due to COVID-19, among seniors.

Dr. Caroline Quach, the chair of NACI, said when the committee's initial recommendation was made, those studies weren't yet available.

However, NACI still says the effectiveness of Pfizer-BioNTech and Moderna from clinical trials is superior and therefore, if there is a choice, seniors should be offered those.

The National Advisory Committee on Immunization now says Oxford-AstraZeneca vaccine can be given to seniors. #AstraZeneca #COVID19 #Covid19vaccine #NACI

Quach said recent studies on real-world use are now suggesting there is no difference in effectiveness between AstraZeneca and the other two, but she said NACI hasn't completed its review of those yet. It is possible NACI will further amend its recommendation on AstraZeneca following that review.

2. How does this align with what is recommended in the United Kingdom and Europe?

The U.K. and the European Medicines Agency both recommended the AstraZeneca vaccine for use on seniors. The U.K. has inoculated millions of seniors with it since the end of December.

Several European nations however, citing the same lack of clinical trial data on seniors, chose not to use it on seniors at first. Many of them reversed that decision because of the same real-world evidence NACI cited Tuesday. That includes France, Germany, Italy, Denmark, Belgium and Sweden.

3. Does this recommendation have anything to do with the concerns in Europe about some patients developing blood clots after receiving the AstraZeneca vaccine?

No. The two issues are completely separate. A number of European nations halted the use of AstraZeneca pending a review of safety data after about three dozen reports of blood clots forming after being vaccinated with AstraZeneca. More than five million doses have been given.

Most of the reports of blood clots were found in people under the age of 50.

Health Canada and the European Medicines Agency are continuing to investigate but say thus far no evidence links the vaccine and the blood clots.

4. What does the new recommendation for seniors mean for Canada's vaccine program?

Initially not a lot. Provincial governments will now have to decide whether they adjust their vaccination plans. All provinces but Quebec had heeded NACI's advice not to use this vaccine on seniors.

The first 500,000 doses were distributed last week. Several provinces used them on people between 60 and 64, British Columbia directed them to high-risk work sites like food processing plants and work camps, while Prince Edward Island targeted restaurant and bar employees between 18 and 29 years old.

Most of the initial doses are already spoken for and Canada has not got confirmed delivery of any more until April, so provinces have some time to reconfigure their plans.

5. What is NACI exactly?

NACI is the national panel of vaccine experts who review scientific reports and results on vaccines, and recommend how various vaccines should be used in Canada.

The panel looks at the evidence and then meets to discuss the evidence and develop joint guidance. There are 16 members and two administrative employees.

NACI is separate and distinct from Health Canada, which regulates the use of pharmaceuticals. Health Canada's pharmaceutical arm will review data on new drugs and vaccines and decide if the data shows them to be safe and effective.

NACI will look more specifically at how a vaccine should be used in Canada. In the case of COVID-19, it looks at all the vaccines available, their limitations such as needing to be ultrafrozen, and decides how best they can all be used to make Canada's vaccination program as efficient as possible.

This report by The Canadian Press was first published March 16, 2021.

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