Ontario Government Authorizes AstraZeneca Use for Second Dose

There are 55,000 doses of the AstraZeneca vaccine that are going to expire in just over a week, but the Provincial government has put a pause on handing out AstraZeneca has a first dose. What do you do? If you’re Ontario’s Chief Medical Officer of Health Dr. David Williams, you authorize the release of those doses for people to receive their second shot of the vaccine.

In an announcement on Friday morning, Williams, along with provincial outbreak response co-ordinator Dr. Dirk Huyer, announced that Ontario residents who received their first dose of the AstraZeneca vaccine between March 10 and March 19 will be able to book an appointment to get their second shot starting May 24. They will have to get in touch with their primary health provider, or the pharmacy where they got the vaccine, to set up an appointment.

“Nothing is more important than the health of Ontarians, and for the best protection against COVID-19 it is vital that everyone who received the AstraZeneca vaccine for their first dose receives a second dose of a COVID-19 vaccine,” Williams said in a statement. “We are providing these individuals with a safe option based on the available data and evidence and will continue to work with Health Canada to monitor the quality and efficacy of all COVID-19 vaccines being used in Ontario.”

There are a couple of caveats though.

First, the timeline between the week of March 10 and the week of May 24 is 10 weeks, and the most recent recommended interval between first and second doses of the AstraZeneca vaccine is 12 weeks.

“We think it’s fine to use the 10 to 12 weeks,” Huyer explained. “Many countries like U.K. were down to eight weeks, so we’re trying to get a combination of utilization of the timing and getting the maximal effect out there to do with the cohorts and different groups we’ve got, we’d still like to go for that 12 week period if we can to make sure people get the maximum peak effect from the vaccination.”

Secondly, there’s still a question about whether the rest of the nearly one million Ontarians who have received a dose of the AstraZeneca vaccine will be able to get a second shot, or whether they will have to wait for the outcome of clinical trials about mixing vaccines. The results from a U.K. clinical trial examining the effects and efficacy of getting two doses from two different vaccines is expected to be published sometime next month.

“When the time comes to receive a second dose, everyone who received a first dose of AstraZeneca will receive either an AstraZeneca or mRNA vaccine for their second dose,” Williams said.

What is certain is that the odds of experiencing vaccine-induced immune thrombotic thrombocytopenia (VITT) are less likely with second doses than they are with first doses. According to the science, the odds of experiencing a blood clot after your first dose of the AstraZeneca vaccine is one in 55,000, but the odds of getting one after receiving the second dose is one in 600,000.

Ontario has handed out over 7.7 million doses of a COVID-19 vaccine, with 4.3 million doses in the month of May alone. On Thursday, the province sent a record for the number of vaccines handed out in one day with 158,524 shots received.

As of Friday, Wellington-Dufferin-Guelph Public Health has handed out 145,812 total doses of the vaccine with 138,607 people having received at least one-dose, which means that 54.3 pr cent of the region has been gotten one shot of one of the three available COVID-19 vaccines. So far 49 per cent of the region’s population between 40 and 44 have received a shot, while 97 per cent of people over 80 have gotten one with 21.2 per cent of those people being full vaccinated.

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