Ok, here it is. Some general information which may help you decide on your second dose when your first dose was AstraZeneca.
633 new cases in Ontario today and I know it's the weekend and some of you will chirp about fewer tests being done on the weekend. Seven day rolling average refutes that theory. It is now 844. It was 4326 on April 22nd. Perspective is stronger than negativity any day.
First of all, NACI, the National Advisory Council on Immunizations, recently approved mixing and matching vaccines. You can receive one dose of mRNA vaccine (Pfizer) as a first dose and another mRNA vaccine (Moderna) as your second and vice versa. You can also receive the AstraZeneca vaccine as your first dose and one of the mRNA vaccines available in Canada as your second dose.
So, how do you choose? Whatever option you choose, two vaccine doses will protect you against COVID-19 and it's variants much better than one. Get two doses. Two doses will protect you against the Delta variant....to some degree. Adhere to physical distancing protocols until they are slowly released. Let's not let this variant get a foothold.
Here's the early data on mixing and matching.
1/ The UK study, mixing AZ with the Pfizer vaccine, involved 830 study participants divided into four groups with each group getting different mixes and matches possible with these vaccines.
Participants who received different vaccines for their first and second doses, regardless of sequence of vaccination, had more side-effects (non-serious ones that resolved on their own) than those who received the same vaccine twice but no safety concerns were noted.
2/ The Spanish study randomized 633 people who received AZ as their first dose and either Pfizer or placebo as a second dose.
Those who received AstraZeneca followed by Pfizer developed twice as many antibodies against COVID-19 as historically seen in people who received two doses of AstraZeneca alone. No safety concerns were identified.
3/ Preliminary data from a German study with only 26 study participants showed that the antibodies developed after one dose of AZ and the second of Pfizer eight weeks later, had neutralizing activity that was 3.9 times greater against the alpha variant ( formerly the UK variant) and similar against the Delta variant ( formerly the variant that originated in India). No safety concerns, a very small number of study participants and not yet peer reviewed. This research is in it's early stages. It can tell us much at all except that it's results may be heading in the same direction as the UK and Spanish studies.
This is important. These studies are small. THE DATA IS NOT YET DEFINITIVE. But, the early data suggests that a dose of AZ followed by a dose of a mRNA vaccine is as effective or more effective at reducing the risk of getting COVID-19 including the alpha and delta variant of COVID-19 with no safety concerns, no cases of clots and possibly more short-term, non-serious side effects after the second dose.
Back to AstraZeneca:
The saga of AstraZeneca’s COVID-19 vaccine has been complicated. Clinical trials and real-world data from the United Kingdom have demonstrated its superb efficacy against severe illness and hospitalizations due to COVID-19. But, the risk of VITT ( that rare but serious blood clot) is 1:60,000 after the first dose of AZ and 1:600,000 after the second. Seventeen cases of VITT have been reported out of 10 million second doses of the AZ vaccine in the UK. That number of people in real world data is massive. We can say with much greater certainty, what the risk of VITT is after the second dose.
This is what you might take into consideration as you make your decision but first and foremost, get a second shot or your will not be protected from the new variants, specifically the delta variant which is circulating in Ontario.
The data around mixing and matching looks very promising but is not yet definitive. More research on more study participants needs to be completed. Biologically, it makes sense that the second dose of a mRNA would be more protective against the variants with no risk of VITT. Early evidence shows this but the final word is not out yet.
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There are many reasons why one might choose AstraZeneca over an mRNA vaccine for their second dose. We know more about this combination. Much more real world evidence is out there, at present, involving millions of vaccinated people.
Your risk of VITT is 1:600,000 with that second dose.
The COM-CoV - United Kingdom study on mixing and matching vaccines, will report data on immunogenicity (antibody response) later this month. It may or may not be supportive of a mixing and matching approach. Some may prefer to wait for this data before deciding. Others may just be happy to take whatever vaccine is available and offered to them first.
Regardless of one’s decision, the critical point is for everyone to get a second dose as soon as they are eligible, whether it be AstraZeneca or an mRNA vaccine. The available evidence gives confidence that both options are safe and efficacious, so there’s no “wrong” choice here. Being fully vaccinated provides optimal protection against current and emerging strains, including the delta variant.
And that's a wrap. I hope this helps.
Anne-Marie
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