UPDATE: On Friday the province announced it will be giving second doses of AstraZeneca vaccines, starting with people who received their first dose of between March 10 and March 19. Those who are eligible are being encouraged to contact the pharmacy or primary care provider where they received their first dose to book an appointment for the week of May 24. The rollout will start in regions where the AstraZeneca vaccine was initially launched in pharmacies in March 2021. Primary care settings and pharmacies may also be reaching out to eligible Ontarians.

“On May 11, 2021, following the advice of Ontario’s chief medical officer of health, Dr. David Williams, the province paused the rollout and administration of first doses of the AstraZeneca vaccine. The decision was made out of an abundance of caution due to an observed increase in an adverse reaction, known as vaccine-induced immune thrombotic thrombocytopenia (VITT), linked to the AstraZeneca vaccine. Ontario is working closely with health experts to continuously review the data for the use of AstraZeneca for first doses. The decision to pause was also based on the increased and more reliable supply of the Pfizer and Moderna mRNA vaccines and the downward trend in cases,” said the province in a Friday news release.

“Choosing to receive the second dose of AstraZeneca at the 10-week interval is safe and provides strong protection against COVID-19.”

ORIGINAL:

Many people who got the AstraZeneca COVID-19 vaccine are wondering what's happening with their second dose.

Niagara's chief medical officer of health says that question should be answered this week – and there are a couple of options.

One is to get a second dose of AstraZeneca.

“We do have more AstraZeneca vaccine coming to Canada,” Dr. Mustafa Hirji said Monday, noting that the bloodclotting issue that raised concerns about the vaccines is not common from a second dose.

“It's really mostly a concern with the first dose of the vaccine. And so there could be an opportunity that people who have got a first dose of AstraZeneca vaccine will be able to get their second dose of that same vaccine later this summer.”

Another option being discussed is getting a second dose of a different vaccine, like Moderna or Pfizer.

He said research is still being done, but early results from the U.K. suggest it is safe, however mild side effects like flu symptoms are more likely.

“Relatively mild side effects, nothing concerning like the clotting issue,” he said.

He noted there isn't enough research yet to be sure, “but I think this will be something that the province will be taking account probably as they make a decision on whether to do second doses with AstraZeneca or do second doses with a different vaccine.”

One challenge is many high-risk people who had AstraZeneca are coming up to their second shot, however research suggests it may be more effective to wait, he said.

Early research from the U.K. on seniors shows a later second dose gave “far better immunity” than an early dose, with three and a half times more antibodies in the people with later doses.

“And so it really does seem like getting a later dose of your vaccine is actually going to give you more protection over the long term and better protection over the long term. But there is a trade-off, of course, it means that in the short term, you're gonna have a little less protection, but you're gonna have a lot more protection longer term.”

“What I'd like to do is actually caution people that it's maybe not necessarily the best thing to get that second dose earlier,” he said.