TORONTO – Ontario is pausing distribution of the AstraZeneca vaccine for first doses.
Health officials on Tuesday said a rise in the number of doses leading to blood clots has essentially doubled, from one in about 125,000 to about one in 60,000.
As a result, the province is also looking into the safety of providing those who have already been administered their first dose of AstraZeneca with an mRNA vaccine like Pfizer or Moderna.
“This decision was made out of an abundance of caution due to an observed increase in the rare blood clotting condition, known as vaccine induced immune thrombotic thrombocytopenia linked to AstraZeneca vaccine,” said Dr. David Williams, Ontario’s chief medical officer of health.
To date the province has administered more than 850,000 doses of AstraZeneca and has a reserve of about 50,000 doses left – with no indication of when Ontario might acquire more supply. Canada has agreements to purchase 20 million doses of the vaccine.
Williams said the initial 650,000 doses had a VITT rate of about 0.9 per 100,000 doses, but in recent days, that number has grown to 1.7 per 100,000, leading health officials to announce the pause.
“In collaboration with public health experts at Public Health Ontario, the Science Advisory Table and our federal, provincial and territorial advisors, we are reviewing the data to consider options for use of the AstraZeneca vaccine for second doses and more broadly moving forward,” Williams said.
“Data from the UK points to a much reduced risk of VITT in second doses of the AstraZeneca vaccine and we look forward to providing more guidance in advance of people needing to receive their second dose of the AstraZeneca vaccine when their time for the second dose comes.”
Williams added the decision to pause is also based on an expected increase in supply of both the Morderna and Pfizer vaccines in coming weeks.
A downward trend in COVID-19 cases in Ontario in recent days has also been factored into the equation.
The blood clots are still rare, said Dr. Jessica Hopkins of Public Health Ontario, but the safety signal was tripped and it was prudent to halt the roll-out.
“What we’ve seen happening over time, and this is very consistent with what’s been seen in other jurisdictions, is we’ve gone from estimates of risk about a month ago… of about one in 125,000 to one in a million risk, to now what we are seeing in Ontario is what equates to a one in 60,000 risk,” Hopkins said.
Williams said the province will turn to federal studies to look at whether or not it’s safe for those who received an AstraZeneca shot as their first dose to switch to Pfizer or Moderna for their second.
“I’ve asked the National Advisory Committee on Immunization to provide direction on the interchangeability of COVID-19 vaccines,” Williams said.
“Based on the much higher risk of COVID-19 infection recently observed in Ontario, including hospitalization, serious illness and death, we maintain that those who receive their first dose of the AstraZeneca vaccine did absolutely the right thing to prevent illness and to protect their families, loved ones and communities.”
It’s not worth the risk, said Ontario’s chief coroner.
“The adverse affect that occurs is a serious effect,” said Dr. Dirk Huyer.
Alberta has paused the use of AstraZeneca vaccines for first doses, saying they don't have enough guaranteed supply to be able to deliver second doses on time. There is a four-month waiting period between shots. The pause is not expected to affect vaccination timelines.
