Certain residents who received their first AstraZeneca dose are eligible to receive their second dose of the vaccine this week.

Residents who received their dose between March 10 and March 19 may opt for an earlier dose interval of 10 weeks, with consent. Residents are asked to contact the pharmacy or primary care provider where they received their dose, and can book an appointment the week of May 24.

“Second doses of AstraZeneca will proceed,” said Medical Officer of Health with the Northwestern Health Unit, Dr. Kit Young Hoon. “The province is planning to release more information on the second dose of AstraZeneca at a later date.”

The province decided to stop administering first doses of the AstraZeneca vaccine on May 11 due to the risk of contracting thrombotic thrombocytopenia, a rare disorder that affects your blood’s tendency to clot. Nearly one million Ontarians over the age of 40 received the vaccine between March 10 and May 11.

Ontario says data from the UK suggests a much-reduced risk of blood clots in the second dose of AstraZeneca, at 1 in 600,000. However, the UK Medicines and Healthcare Products Regulatory Agency’s data previously listed the risk of blood clots from the first dose at 1 in 250,000, which was later reported at 1 in 60,000 in Ontario.

“For people who received AstraZeneca in our catchment area, they made the right decision,” explained Young Hoon. “They chose the vaccine that was available earliest to them, at a time when vaccine supply was very uncertain.”

Ontario is also looking at the administration of two doses of different vaccines, and has requested further direction from the National Advisory Committee on Immunization. At this time, they do not recommend that vaccines of different types be used, as data on mixing vaccines is not available yet. Results are expected, however, by June.

Despite not having the results or data available, Ontario says everyone who received a first dose of the AstraZeneca vaccine will receive either an AstraZeneca, Pfizer or Moderna vaccine for their second dose.

“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,” said Chief Medical Officer of Health, Dr. David Williams.

“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.”

Ontario notes as of May 25, individuals will be able to log-in to the provincial portal to obtain a PDF copy of their COVID-19 vaccination receipt for both their first and second doses.