Editor’s note: This is an evolving story. As of May 11, both Alberta and Ontario have paused the use of the AstraZeneca vaccine. Click here for our most recent coverage of the vaccine.
Ontario and Alberta are offering the AstraZeneca-Oxford COVID-19 vaccine to people 40 years of age and older starting today.
As pharmacies and family doctor offices gear up to give this two-dose vaccine to more and more Canadians, here are five things we all need to understand about it.
1. This vaccine is very effective at preventing severe illness, hospitalization and death due to COVID-19
Data from clinical trials on AstraZeneca show that the vaccine is nearly 100 per cent efficacious in preventing severe illness, hospitalizations and deaths. Real-world data from the U.K. – where the majority of citizens received AstraZeneca – confirm the drastic decline in hospitalizations and deaths due to COVID-19 post-vaccination, where the dominant strain is B117. This data is extremely reassuring to us here because the B117 is currently the dominant variant in Ontario.
2. There is a very small, but real, increased risk of side effects
The AstraZeneca vaccine has been associated with rare but serious blood clots accompanied with thrombocytopenia (low platelets). This has been termed Vaccine-induced Immune Thrombotic Thrombocytopenia or VITT. The European Medicines Agency observed six cases in 6.8 million doses, for an event rate of under one per million doses. In the Canadian context, we have seen two cases after more than 500,000 doses of the vaccine. The absolute risk for these events remains low overall.
Individual risk is not the same as absolute risk and can be higher or lower depending on age or gender, among other factors. For example, the risk of VITT might be higher than one per million in women under 30. Globally, the majority of these events occurred in women in the 20 to 55 age group and typically within four to 20 days post-vaccination. VITT is treatable if detected early.
3. The benefit of AstraZeneca substantially outweighs the risk during this third wave
Nearly everything in life is a balancing act between risks and benefits. But we are more likely to take calculated and informed known risks than new ones. For example, we hop into our cars every morning to drive to work despite the fact that fatalities due to motor vehicle accidents number 50 in a million annually (and that doesn’t include injuries).
In Ontario, we are on the brink of a health-system collapse. Our ICUs are admitting younger and younger patients. Field hospitals are being set up and pediatric ICUs converted to treat adults. Given the degree of community spread of COVID-19 variants in Ontario, there is a real risk of getting a variant that must be considered in any risk-benefit calculation around vaccines. As well, the vaccine not only provides individuals with protection but also indirectly protects those around them.
The Winton Centre for Risk and Evidence Communication modelled UK data to illustrate the differences between the benefits offered by the vaccine and small risks of adverse effects. In every situation, including those with low COVID-19 exposure risks, the benefits of AstraZeneca outweigh the risks in those over the age of 30 because the risk of severe COVID-19 infection increases with age.
In Ontario, we are approaching an incidence similar to the high-risk modelling shown in the chart, where the benefit for those over 40 is substantially higher than the risk of side effects:
Even in medium- and low-exposure risk scenario modelling, the benefit is substantial as age increases. However, for those under the age of 30, the risk-benefit changes in a low COVID exposure situation.
4. The pause in use does not mean the vaccine is unsafe
The National Advisory Committee on Immunization (NACI) recommendation to pause use of the AstraZeneca vaccine on March 29 was not a confirmation it is unsafe or that approvals were rushed. It is almost impossible to identify such rare side effects in a clinical trial setting. It is only with real-world use of a vaccine in millions of people that you can identify rare reactions.
The brief pause in use for people under 55 is due diligence, done to take all adverse events seriously and ensure COVID-19 vaccine safety.
Pausing use allowed us to better understand real-world data, including incidence and risk of these rare clots. It also served to increase health-care provider and public awareness, ensuring complications can be swiftly recognized and treated appropriately if they occur.
5. Bottom line? Take the first vaccine that is offered to you.
Demand for vaccines is high going into the third wave, and rightly so. But the real-time reporting around the AstraZeneca vaccine and its rare side effects has been confusing for the public. It’s important to not only address safety concerns with empathy and understanding, but also to communicate that due diligence is being done on all vaccines authorized for use in Canada.
The AstraZeneca vaccine is highly effective in preventing severe illness, hospitalization and death due to COVID-19. While it is not risk free (few things in life are), it is safe. And the risk of becoming severely ill with a COVID-19 variant is real. Our advice is to take the first vaccine that is available to you.