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Ontario to give 2nd doses of AstraZeneca vaccine

The hundreds of thousands of Ontarians who got a first dose of the AstraZeneca vaccine will be able to get a second dose.

The province's chief medical officer of health announced Friday morning that second doses of the vaccine will be made available to those who got a first dose. Dr. David Williams said the second dose campaign will begin with those who got their first AstraZeneca shot between March 10 and March 19, 2021.

“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,” Dr. Williams said in a statement released Friday. “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.”

The province halted the first dose rollout of the AstraZeneca vaccine on May 11, citing concerns about the risk of blood clots. The decision came in the wake of data that showed the risk of vaccine-induced thrombotic thrombocyctopenia (VITT) and was made out of what the province called "an abundance of caution," as well as a more reliable supply of Pfizer and Moderna vaccines and the downward trend in the number of COVID-19 cases.

The decision to offer second doses comes as data from the United Kingdom suggests the risk of VITT is much lower (one in 600,000) after the second shot.

"For a limited time during the week of May 24, individuals who received their first dose of AstraZeneca during the period of March 10, 2021 to March 19, 2021 may opt for an earlier dose interval of 10 weeks with informed consent," a statement from the province said. It added the province is working with pharmacies and primary care providers to make sure second doses for others who got their first AstraZeneca dose are able to make appointments for the second within the 12 week interval. It says it will provide information on how that will happen in the near future.

The province also said Friday that it is looking at available data from a clinical trial in the U.K. that is examining the mixing of doses. It is asking for direction from the National Advisory Committee on Immunization, which has not recommended that vaccines of different types be used in a two-dose series of innoculation.

"The province will provide further guidance with respect to administering doses of two different vaccines in the near future and in advance of the 12-week interval when most people are needing to receive their second dose of the AstraZeneca vaccine," a news release from the province said. "When the time comes to receive a second dose, everyone who received a first dose of the AstraZeneca vaccine will receive either an AstraZeneca or mRNA vaccine for their second dose."

Ontario currently has thousands of AstraZeneca doses that are set to expire in the coming days. It's expecting shipments of hundreds of thousands of doses in the near future.

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