How likely are people to suffer serious side effects having been vaccinated?
Complications associated with the COVID-19 vaccines have left members of the public concerned. How likely are people to suffer serious side effects having been vaccinated? Kelly Grindrod, a pharmacist and professor, provides answers to this and other questions.
Is it okay that I got AstraZeneca as my first dose?
All four vaccines approved in Canada—AstraZeneca, Johnson & Johnson, Pfizer and Moderna—are extremely effective at protecting against severe illness, hospitalization and death. The many, many Ontarians who have managed to get a first dose of AstraZeneca gained protection from COVID four to eight weeks ahead of when they were expected to be vaccinated. Emerging research is showing that a single dose of AstraZeneca appears to offer similar protection to a single dose of Pfizer against hospitalization, and also seems to reduce contagiousness pretty well. That means people who got a first dose of AstraZeneca not only protected themselves but protected the people around them too.
The “safety signal,” or the rare but serious clotting side effect that has emerged with AstraZeneca, has prompted the National Advisory Committee on Immunization (NACI) to identify the Pfizer and Moderna vaccines as “preferred” when the risk of COVID is lower. Expect this to be an ongoing conversation in the coming weeks and months.
Can you explain the rare but serious side effect of the AstraZeneca vaccine?
We continue to learn more about the rare but serious side effect called “vaccine induced thrombotic thrombocytopenia (VITT).” There are two viral vector vaccines approved in Canada—AstraZeneca and Johnson & Johnson. Both appear to cause VITT. Pfizer and Moderna are mRNA vaccines and do not appear to cause VITT.
According to the latest available data, the risk of VITT with AstraZeneca appears to be around one to two people per 100,000. The risk with Johnson & Johnson may be lower, at around one in 500,000. Canada has administered over two million doses of AstraZeneca in the last month, meaning we should expect to see approximately 20 to 40 cases of VITT in the coming days and weeks. This compares to the approximately 40 COVID deaths we see daily in Canada right now.
VITT is different from a normal clot. It is a very serious reaction where the body forms antibodies against platelets 4 to 28 days after an AstraZeneca or Johnson & Johnson vaccination. This leads to multiple clots, low platelets, and bleeding. Younger women may be at slightly higher risk, but it can occur at all ages and in all genders. Most cases have been after the first dose. Here is a useful FAQ document from Thrombosis Canada about VITT.
Canada is getting a lot more Pfizer. What does that mean for us?
Two things have changed recently in Canada with regards to the Pfizer COVID vaccine—a huge increase in shipments and approval for kids aged 12 and older.
Pfizer has indicated that it is dramatically increasing its vaccine shipments to Canada, sending us over two million doses a week starting in May. This news speeds up our vaccine timelines. The Canadian government now predicts we can vaccinate every Canadian who wants a vaccine by July 1. This is also likely to speed up the time to second doses, as more Canadians may be able to get their second doses in the summer.
The other news was the approval of Pfizer for children aged 12 and older. In March 2021, Moderna also began a trial in children as young as six months. We expect news about kids aged six months to 11 years in the summer months. This means that older kids may be fully vaccinated early in the school year while younger kids could be a few months behind.
If I got AZ as my first dose, can I get a different vaccine for my second dose?
Canada has just announced a new shipment of AstraZeneca later this month, with most doses destined to be second doses. The risk of VITT appears to be lower for the second dose than the first dose. The COM-COV study in the UK is also looking at the effects of mixing vaccines, including various combinations of AstraZeneca, Pfizer, Moderna, and Novavax. The research aims to identify if there is any advantage to mixing vaccines, including if there is a stronger immune response. The studies are also looking at side effects and safety. We expect to start seeing some early results late May into June. This may give people who got a first dose of AstraZeneca some options in the months ahead.
