Since Ontario halted the distribution of first doses of the AstraZeneca-Oxford COVID-19 vaccine, close to one million people have been left to wonder when they'll get a second dose.
Dr. David Williams, Ontario's chief medical officer of health, now has a few answers.
Who is eligible?
On Friday, Williams announced the province will soon be distributing some 55,000 doses set to expire May 31.
Eligible Ontarians are those who were among the first cohort aged 60 to 64 vaccinated between March 10 and 19 as part of a pilot project involving 325 pharmacies in Toronto, Windsor and Kingston.
Physicians in six public health units — Hamilton, Toronto, Wellington-Dufferin Guelph, Peterborough, Simcoe Muskoka and Peel — also distributed vaccines during the pilot.
How do I get my dose?
People eligible for the second dose should reach out to the location where they received the first one.
Some participating pharmacies may also begin sending out notifications directly, said Justin Bates with the Ontario Pharmacists Association (OPA).
Not all of the 325 original pharmacies will be giving out second doses, said Bates. According to the OPA, anyone whose pharmacy is not participating will be given the opportunity to reach out to another that is taking part.
Is it safe to get the dose now?
There's growing research about the best time to get the second AstraZeneca shot.
The latest suggests the vaccine is at its peak efficacy after 12 weeks, reaching 89 per cent effectiveness against COVID-19 and rivalling the rates of the Pfizer-BioNTech and Moderna vaccines.
But next week's rollout plan would see those vaccinated on March 19 getting a second dose with only a 10-week interval, placing efficacy closer to 70 to 75 per cent.
Williams said the difference is "negligible," but people should consult with a health-care provider or pharmacist in order to make an informed decision.
As for severe adverse effects, the risk of a blood clot from a second dose of AstraZeneca is one in approximately 600,000, said Williams. That's significantly lower than the risk from a first dose.
Are there enough doses?
While there are 55,000 doses available, the OPA estimates 90,000 Ontarians received a dose at a pharmacy during March 10-19.
"So it will really depend on, out of those 90,000 people, how many are actually going to want to get the AstraZeneca second dose early at the ten-week interval," said Bates.
In addition to the expiring doses, however, the province has also been receiving some 254,500 new doses of AstraZeneca this month.
Williams said anyone was first immunized between March 10-19 and does not get their second dose next week can book that dose for the twelfth week after their first shot.
Can I get a Pfizer or Moderna 2nd dose?
Williams said the province is still waiting for advice from the National Advisory Committee on Immunization (NACI).
Early research suggests that a second shot of an mNRA vaccine like Pfizer or Moderna as the booster for AstraZeneca is not dangerous, but Williams said he's waiting to hear whether the combination offers the same efficacy as a second AstraZeneca dose.
A recommendation from NACI is expected in early June.
What if I got AstraZeneca after March 19?
Ontarians vaccinated with AstraZeneca before March 19 represent a little over 10 per cent of the province's total AstraZeneca recipients.
Williams said the plan for those vaccinated after March 19 depends on the science and the supply.
"We need about another 750,000 doses," said Williams, adding future supply is uncertain and that doses could be redistributed among the provinces.
If NACI does say it's OK to replace AstraZeneca with Pfizer or Moderna for the second dose, that could be part of the solution, Williams said.