AstraZeneca now or wait for Pfizer?


  • both vaccines great, and unless you are told by a specialist or your doctor that you can’t have one for a very specific reason
  • get the one you can get today or tomorrow


I think we see a lot of emotion on social media about what people should do. It’s a hard choice for a lot of people to make, especially when we’re trying to weigh up potential risks, and the outcomes can mean very different things to different people.

I am not going to say you should do one or the other in this, but I will outline some points that might help you decide what you want to do.


Risk of catching COVID-19

Back on the 13th of July 2021, ATAGI released a statement on the use of COVID-19 vaccines in an outbreak setting.

It almost seemed like a simpler time, but on the 13th of July we had 72 cases, 59 of which were local, and 13 under investigation. We had vaccinated 20,749 people that day, and 2,053,904 had received at least 1 dose, with 710,714 of those had been fully immunised.

The statement above says that the cumulative risk of contracting COVID-19 until the 11th of July was 10/100,000 in greater Sydney, but that risk increased by 2/100,000 per day.

In the Fairfield LGA it was >100/100,000 and increasing by >10/100,000 per day.

Now cumulative risk appears to be a rather tricky number to calculate, and without knowing what factors were included to arrive at that figure I can’t give you an accurate one as of today. But assuming nothing had changed (the biggest change is obviously the number of daily cases – known and unknown in the community – and the mobility of people) the risks of contracting COVID-19 on the 2nd of September 2021 should be as follows.

  • 118/100,000 in Greater Sydney
  • >640/100,000 in LGA of concern (Fairfield used as the calculation)

Seeing that the population of Greater Sydney is approx. 5,312,163 then about 6268 people are at risk of contracting COVID-19. If you live in Fairfield LGA which has a population of 198,817, then 1272 people in Fairfield are at risk of contracting COVID-19.

Now I know that these numbers all depend how much you might run into other people, if you are at a workplace, if you’ve been immunised, if you’re wearing a mask etc. But it’s a ballpark start.

The reason I rant about it, is when ATAGI suggested the benefits of receiving AstraZeneca outweighed the risk of any rare side effects (namely TTS) – the risks were about 11.8x lower in greater Sydney, and 6.4x lower in Fairfield LGA. So, the recommendation of AZ as a vaccine choice is clear now.


But Pfizer is almost here! Maybe.

Maybe. Our GP clinic was a pilot site for rolling out Pfizer to the community, so had a big head start on a lot of other GP clinics who will be receiving their first Pfizer around the 13th of September. And yes, while increased amounts are given to the State Hubs and GP clinics each week – the people who are included in eligibility are expanding also – meaning the individual booking slots aren’t as available as we’d like.

Every time, I hear or read about eligibility opening up, I am both happy it’s happening, then super frustrated I find out at the same time as everyone else. We usually then have to go find the details that it’s not actually for a few more weeks that eligibility has been expanded.

But when we go to order more stock – there are no increased quantities made available. For the past few weeks, we’ve not been able to order any more stock despite the system at our clinic being setup to deliver 100 doses per hour (with a monster effort from our team), and the ability to do this all week long if we had the stock.

Now, if we think back to the COVID-19 vaccine allocation horizons (what ever happened to that war room?) we may or may not get 50,000 – 250,000 extra doses in September Australia wide. And in October there will be quite a bit more.

And at the same time a whole big group of the population became eligible – which is bloody fantastic – but without the doses needed – you might still be waiting a while for your first dose, let alone your second. And all this while trying to avoid contracting COVID-19 which can happen literally in seconds.


But I don’t really go outside most of the time.

I think it’s pretty clear Delta spreads very easily. Fleeting contact, mere seconds. But it’s hard to be so isolated that you don’t have any contact at all. The public health unit takes exposure pretty seriously, and even when a COVID-19 positive patient has a surgical mask, spends about 20 seconds talking to another person who is wearing a surgical mask – they will consider it a close contact and make you isolate for 2 weeks. They’re this strict, because we’re still trying to get to really high numbers of fully vaccinated people. So, if you do happen to talk to people or go past them – like in the office, at the factory, on a bus, at the supermarket, in a lift, while getting your coffee – you’re not really 100% safe – though no one really is. So, the question is, what will get immunity in my body faster?


There is no shortage of AstraZeneca – and almost everyone is eligible – risks are low

This kind of makes it really easy. If you’re 18 and over – you’re eligible. No declaration forms, no paperwork from your doctor. The risk of clotting (TTS) is low as we know, and in the latest ATAGI update the risk of TTS was 2.6/100,000 first doses in people under 60, and 1.8/100,000 first doses in people 60 and over.


Isn’t it faster to wait for Pfizer? I’ll have both vaccines before I get 2xAZ

Not necessarily.

Most NSW Health run hubs now have about an 8 week wait between your first and second doses of Pfizer, in order to allow more people to get their first doses, and to deal with the priority groups for vaccination, shortages of vaccines and many other complicated and shifting factors. Some GP clinics might still be offering a 3 week wait between doses, but this depends on their allocations and booking systems. For example, at our clinic, we only open appointments when we know we have the vaccine in the fridge. So, if there’s a delay – you might be waiting.

AstraZeneca can be given in as little as 4 weeks between doses (28 days to be more specific). And seeing that the state hubs and many GP clinics have plenty in the fridge, you will almost be able to get AZ any day of the week.

I have been immunised with 2 doses of AstraZeneca, and so have many other GP’s, nurses, and GP clinic staff. Everyone on our team that received AstraZeneca is under 40, and the majority of patients that attend our clinics for the AZ are under 40 as well. From when it was announced AZ was ok for under 40 from the PM – 63% of all AZ given at GSH were in patients aged 18-39, and a further 22% were 40-59. So, a whopping 85% of AZ recipients were 59 and under. This is from 2712 people for 2305 doses in people 59 and under.


So, what should I do?

I know it doesn’t make the decision for you – but you should get the immunisation you can, as soon as you feel ready. If you need an immunisation to be able to go to work and only AZ is available? Get AZ.

If you have had a rare condition like Heparin Induced Thrombocytopaenia? Get Pfizer.

If this week you can get either, or the second dose is soon – pick the date most convenient for you.

There is no “better vaccine”. They both reduce the risk of contracting COVID-19, they both reduce the risk of severe disease significantly. The published statistics by how much they prevent these are measure from a few factors. Like antibody levels, and how many people in a group they tracked contracted covid after vaccine dose 1 and 2, and how many who didn’t get the vaccine contracted covid.

But in reality, the amount of protection a vaccine provides for an individual will be on top of other measures they are doing – like staying away from people, wearing masks, washing hands, ensuring airflow is good wherever you are.

TL: DR – both vaccines great, and unless you are told by a specialist or your doctor that you can’t have one for a very specific reason – get the one you can get today or tomorrow.

Written by Dr Daniel Chanisheff on the 2nd of September 2021.