Can You and Should You Mix COVID Vaccines? What Happens When You Get Two Different Jabs

Mixing vaccines

With everyone in the country now allowed to get the AstraZeneca dose of the vaccine, and supplies of that particular type coming in thick and fast to the country, there are now questions around what happens if you end up getting two different kinds of jab.

On the surface, it might seem like a bad idea. Almost all the vaccines we have are designed to work on a two-shot basis, with only Johnson & Johnson, a type that Australia has no plans to buy, offering a one-shot fix.

You would think that each shot is reliant on the other in order to teach the body how to properly defend against the coronavirus but that might not actually be the case.

The current Australian health advice does not recommend getting two different shots of the vaccine, however, Dr Norman Swan has previously suggested that there might be good evidence to get one of each.

Now, a new study from the University of Oxford — the home of the AstraZeneca vaccine — has shown that getting a shot of both Pfizer and AstraZeneca might actually be more beneficial than getting two doses of either.

Can you mix and match COVID vaccines?

The unofficial answer, at least for the vaccines available in Australia, is that you can.

A Spanish trial found that getting a dose of Pfizer after a first dose of AstraZeneca can produce a “robust immune response”.

A similar study in Germany has also found that having Pfizer after AstraZeneca was more effective than just AstraZeneca alone.

Research into vaccine combinations is still in its infancy however and there is not enough clear data to prove that one method of vaccination might be better than another. The question then is, why would you do it?

The government has not made things easy with its confusing messaging around AstraZeneca. Initially, the vaccine was supposed to be our workhorse vaccine, the one that all of us would be getting.

That then changed after evidence of very rare blood clots emerged in younger people. The government then shifted its rules to only allow people over the age of 50 to get AstraZeneca while the rest of us would be getting Pfizer.

That then changed again after new information showing blood clotting in people over the age of 50 forced the government to shift the age criteria higher to people over the age of 60.

The fact that we have so much AstraZeneca on order, and with millions of people wanting to get vaccinated who currently can’t, the government recently changed its advice yet again to say that all Australians who want AstraZeneca can get it.

People who are naturally concerned about the blood clotting risks and who might have had the first dose of AstraZeneca have been reported to be avoiding getting their second one out of fear.

It’s a natural thing to be afraid of but not one that is very likely to happen. The chances are less than one in a million meaning there is a far greater risk of dying in a road traffic accident than of the vaccine and we all get on the roads without a second thought.

It’s not the only reason though, as new information suggests it might actually be beneficial to mix and match your vaccines.

Mixing Pfizer and AstraZeneca

New research from scientists in Oxford looked at the impact of a mix-and-match approach to vaccinations where people were given either two shots of AstraZeneca or Pfizer or a combination of the two.

They found big differences in antibody levels depending on the shots given.

While two doses of Pfizer produced the highest levels of antibodies, one shot of AstraZeneca followed by a Pfizer shot was almost as good.

The order of the vaccines makes a big difference. Those who had a Pfizer shot and then an AstraZeneca had seven times fewer antibodies than those who had two shots of Pfizer.

This is still five times higher than those who had had two shots of AstraZeneca, however.

“You’ve certainly got an extra kick to your immune system if you boost with the RNA vaccine from Pfizer rather than a booster dose of the AstraZeneca vaccine,” said Matthew Snape, the chief investigator on the Com-Cov trial and associate professor in paediatrics and vaccinology at Oxford.

Based on the findings, the UK is considering whether or not to offer different vaccines as boosters in the Autumn. Most of the UK will have received the AstraZeneca shot and these findings suggest that topping it up with a Pfizer shot could be more effective against COVID.

“Based on what we’re seeing here, switching over to an RNA vaccine could have some benefits in terms of antibodies,” said Snape.

Should you get your second dose of AstraZeneca?

Australia’s official advice is that if you’ve already had your first dose of AstraZeneca without issues, you should also get AstraZeneca for your second dose.

Data from the UK suggests that the risk of blood clots from AstraZeneca is still extremely low.

More than 17 million people in the UK have had two doses AstraZeneca and only 27 developed cases of blood clotting afterwards.

That makes your chances about one in 1.5 million.

We’re also a lot better now at detecting the types of blood clots that this vaccine can cause and treating them too.

If you’re offered a vaccine of any kind, you should take it. Let’s open Australia up.

Read more stories from The Latch and follow us on Facebook.