Ontario pauses first doses of AstraZeneca over clot concerns
May 12, 2021
Ontario is pausing first doses of the AstraZeneca COVID-19 vaccine out of an “abundance of caution” after a recent increase in rare blood clots, and is doing further research on a plan for second doses, says chief medical officer Dr. David Williams.
The move follows eight cases of vaccine-induced immune thrombotic thrombocytopenia (VITT) in the province among almost 854,000 recipients of AstraZenca and related Covishield jabs administered since early March -- including to Prime Minister Justin Trudeau, Premier Doug Ford and Health Minister Christine Elliott.
There have been no VITT-related deaths reported in Ontario but three women have died in other provinces.
Williams told a Tuesday news conference the decision was also based on increased supplies of Pfizer and Moderna vaccines along with a “recent downward trend” in COVID-19 cases across the province, making it prudent to eliminate the risks that AstraZeneca could pose to some people.
“The context has changed,” said Dr. Jessica Hopkins, head of health protection and emergency preparedness at Public Health Ontario.
The step back will not hamper the province’s target of having 65 per cent of adults vaccinated by the end of May, said chief coroner Dr. Dirk Huyer, co-ordinator of provincial outbreak response. With just 50,000 doses left, AstraZeneca was not factored in to that calculation.
Hopkins said the estimated risk of VITT clots has recently increased to one per 60,000 people vaccinated in Ontario, up from previous estimates of one in 100,000 and lower.
“That’s a significant safety signal we don’t want to ignore ... It takes many doses before you see it,” she added.
“One of the things that I don’t want to happen is for people to misinterpret this. This is still a very rare side effect ... The reason that we’re talking about this is because it was one in 100,000 before.”
The national rate is slightly higher than Ontario’s at one in 55,000 cases and the science table of experts advising Ford published a paper Tuesday saying the frequency may be “underestimated” in the province.
The decision leaves thousands who have booked AstraZeneca appointments at pharmacies scrambling to get other shots.
Also Tuesday, Alberta said it would no longer give first doses of the AstraZeneca vaccine due to uncertainty about future supplies.
Symptoms of VITT typically show between four and 28 days after the shot, and physicians and hospitals have been advised on signs and treatments.
Ontario officials said those who rushed to get AstraZeneca vaccinations in pharmacies as the third wave built and crested since March still did the right thing -- a sentiment echoed by University of Ottawa epidemiologist Raywat Deonandan on social media.
“If you got the AZ jab: (1) you didn’t make a mistake; you got great protection when others did not; (2) you helped drive incidence down to the point where we have the luxury of vaccine choice; (3) you will likely get boosted by an mRNA vaccine, which will be just fine,” Deonandan wrote.
Williams confirmed there will be the option for people who got first doses of AstraZeneca to receive second doses of the Pfizer or Moderna vaccines, pending results from an upcoming study in the U.K. on mixing vaccines and advice from the National Advisory Committee on Immunization.
The province will now review data on AstraZeneca to determine further use of the vaccine and noted information from the United Kingdom -- where it has been used broadly -- shows a “much reduced” risk of clots at the rate of one per million after second doses.
“If we’re going to be asking people to participate in a second dose on that one, it’s with information that they can make the decision,” Williams said.
Public Health Ontario will be looking closely at side effects from second doses in the U.K. and elsewhere.
The race is now on for Ontario health officials to study the data and nail down recommendations before people who got AstraZeneca become eligible for second shots starting in July.
With future supplies of AstraZeneca less clear than others, it is possible that it may be faster for some people to get a Pfizer or Moderna booster, Williams said.
“We hope to have those answers in the next few weeks,” he added. “We’re also seeing early promising results of administering two doses of different vaccines.”
In Ottawa, Intergovernmental Affairs Minister Dominic LeBlanc said the country is expecting 665,000 doses of AstraZenca by the end of May and another one million in June. Ontario would get about 40 per cent of that supply based on its population.
In the legislature before the AstraZeneca pause was announced late Tuesday afternoon, New Democrat Leader Andrea Horwath pressed the government for more details on second shots for people who got the vaccine.
Thousands who received it at pharmacies in the early days still do not have second appointments, unlike others who have gone to mass vaccination clinics for Pfizer and Moderna.
“People are anxious to know,” Horwath said.
Meanwhile, Ontario is moving closer to offering Pfizer vaccinations to children aged 12 to 17, but they will have to wait until shots for COVID-19 are offered to older age groups, Solicitor General Sylvia Jones said.
Waterloo Region kick-started the process by opening registration for teens Tuesday with the proviso that “it may take four to six weeks to be contacted for an appointment -- when it is their turn.”
Jones said no dates have been set province-wide because the government is checking with local public health units to gauge supply of Pfizer vaccines and upcoming bookings for adults to determine time lines.
She suggested teens won’t be able to make appointments until after the week of May 24, when about 940,000 doses of Pfizer are expected to be shipped to Ontario weekly until the end of June.
“We will get there,” Jones told reporters. “We are very excited and intend to move very quickly.”
Health Canada approved Pfizer for ages 12 to 15 a week ago, clearing the way for provinces to begin administering doses. It is the only vaccine cleared for children that age, although Moderna is expected to seek approval as well.
In terms of the overall vaccine rollout, Jones said health units outside designated COVID-19 hot zones can expect a boost in supply next week because doses will be shipped based on population levels. For the last two weeks, 50 per cent of vaccines have been targeted in hot zones to quell high rates of transmission.This should allow many health units to expand the hours and days that vaccination clinics are open as the province aims to have first doses into 65 per cent of adults by the end of May