Mixing, matching of vaccines gets green light

It’s official: when it comes to vaxxing, the National Advisory Committee on Immunization (NACI) has given the green light to mixing and matching.

As Canadian provinces begin to roll out second doses of COVID-19 vaccine, many of us have wondered whether we’d have to dance with the one who brought us — in other words, stay with the same vaccine for both the first and second dose — or whether we could change partners mid-reel.

NACI announced this week that the latter works just fine, whether you’ve received a first dose of messenger RNA (MRNA) vaccine like Moderna or Pfizer, or a vector vaccine like Astrazeneca.

NACI, which provides advice on immunization practices to the Public Health Agency of Canada, says vaccine products have often been used interchangeably in the past to protect against illnesses, including hepatitis A, influenza, measles and mumps.

But because of the blood clot issue linked to the Astrazeneca vaccine, some countries were advising health officials to follow a first shot of AZ with a different type of vaccine in order to minimize the risk. In light of this uncertainty, Canada’s public health agency looked to NACI for advice on best practices.

NACI considered studies on mixed doses conducted in the United Kingdom, Germany and Spain. While it recommends that if your first dose was an MRNA vaccine, the preferred No. 2 shot would be the same product, it says if your first shot was Moderna, say, and your only option for the second dose is Pfizer (or vice versa), that’s fine too.

People whose first shot was AZ can go with either AZ, Pfizer or Moderna as their second shot.

However, anyone who experienced a blood clot believed to be connected to their first shot of AZ should go with an alternate vaccine as a second shot. The risk of the type of blood clot linked to a first AZ shot in Canada is estimated to be one in 83,000 people, though NACI says, “as investigations continue, the rate could be as high as one in 55,000.”

Let’s hope that knowing doses can be safely mixed reassures Canadians who might have been hesitant to receive a second shot of Astrazeneca after having received it as a first shot.

Another piece of positive news? NACI reports that while recent Canadian surveys have shown that more people are comfortable receiving an MRNA vaccine than a viral vaccine, more and more people are showing a willingness to be vaccinated, period.

“The most recent Canadian studies report that intention to vaccinate is increasing and currently varies between 66 to 80 per cent in the general public and 57 to 82 per cent in health-care workers across Canada,” NACI said.

That’s good news for us all. Shots all around!