Health experts issue a strong warning against mixing vaccines

Australians over 60 wanting the Pfizer COVID-19 jab could die waiting, says Australia’s peak medical body.

The warning comes as a growing number of older Australians who received an AstraZeneca vaccine are putting off getting their second jab in favour of waiting for more doses of the Pfizer vaccine to hit our shores.

Many older Australians don’t want the AstraZeneca vaccine because they view the Pfizer vaccine as superior, says Australian Medical Association (AMA) vice-president Dr Chris Moy.

“There’s a belief that over-60s have been cast off and are second-class citizens,” he says.

“People have this perception of it being unfair, why am I being treated differently from a younger person?

“But AstraZeneca is a very effective vaccine and the other thing to keep in mind is the reason why the decision was made is the risk of thrombosis thrombocytopenia syndrome (TTS) drops as you get older.”

Read: Older Australians waiting for mRNA vaccines at back of the queue

German research suggests that mixing one dose of AstraZeneca with either Pfizer or Moderna could result in a stronger immune response than having two doses of the AstraZeneca vaccine.

Similar studies found that a mix of AstraZeneca and Pfizer generated a strong immune response against the virus. When AstraZeneca was followed by Pfizer it induced “higher antibodies and T-cell responses than Pfizer followed by AstraZeneca”.

However, Doherty Institute Professor Dale Godfrey told newsGP that the combination may induce a greater immune response but he is not convinced the approach will prove more protective against variants.

A Guardian report stated that the Australian Technical Advisory Group on Immunisation (ATAGI) says evidence is strongest for receiving two doses of the same COVID vaccine.

“At the moment, the ATAGI advice and the advice from the Therapeutic Goods Administration, the regulator for medicines in Australia, is that a full course of COVID vaccination is two doses of the same vaccine – two doses of Pfizer vaccine or two doses of AstraZeneca,” says the Department of Health‘s COVID-19 primary care response first assistant secretary Dr Lucas de Toca.

“Preliminary data shows that there might be some benefit and there might be some potential for these [mixed dosing] regimes to be used in the future; however, this is very early at the moment, we’re talking about small studies, not clinical efficacy or effectiveness in the real world.

“At this stage, the advice from our experts is that a full course is two of the same vaccine.”

Read: Mild side-effects to long-term protection: How COVID-19 vaccines work

The advice in non-outbreak settings is that the Pfizer vaccine is the preferred vaccine for those under 60, but many have opted to receive the AstraZeneca vaccine in current outbreak settings.

Those awaiting second-dose AstraZeneca appointments who think they have a shot at Pfizer will be disappointed regardless of how many extra Pfizer doses arrive in coming months, according to health authorities.

“Our advice is mixed dosing is not approved in Australia and we are proceeding as per ATAGI guidelines,” says the head of the Royal Australasian College of General Practitioners (RACGP) Dr Karen Price.

“I am not quite sure what people are concerned about given recent studies on AstraZeneca showing good results, and the second dose is linked with hardly any TTS.”

AMA head Dr Omar Khorshid says “there are definitely people vaccinated with AstraZeneca interested in getting Pfizer as a second dose, but that really doesn’t make any sense”.

“The majority of the small risk of TTS is associated with the first dose and, in addition, vaccination with AstraZeneca may also provide better longer-term protection than Pfizer,” he says.

“For those who have had their first dose of AstraZeneca it’s a no-brainer to have the second. It’s a fantastic vaccine with excellent efficacy and safety. The studies on mixing vaccines are much smaller.”

Read: Business figures turned to Rudd to bring forward Pfizer vaccine

ATAGI co-chair Professor Allen Cheng says minimal evidence suggests receiving mixed vaccines may be beneficial, is effective, and seems to be safe, but more work is needed to understand the best timeframe between dosing when mixing vaccines.

“The clinical trials for two doses of the same vaccine have tens of thousands of people, and many millions of people have received two doses of the same vaccine, whereas the experience with mixed schedules is much more limited,” he says.

“We have provided some early advice on the use of different vaccines in clinical situations where this is necessary.

“For example, people who have had a serious reaction to the first dose of one or the other vaccine, or people who have received a vaccine overseas that is not available in Australia. In terms of making mixed schedules available routinely, we note that while supplies of one vaccine are still constrained it probably isn’t possible to offer a choice to consumers.”

State premiers and health authorities are concerned vaccine messaging is becoming increasingly confused and are urging Australians to show up to their existing first and second-dose appointments as they stand.

“The best vaccine … is the one you can get today,” says Victorian Premier Daniel Andrews.

“There are literally thousands of AstraZeneca appointments available for you [right now].”

Read: Get whatever vaccine is available, advisory group warns

NSW health minister Brad Hazzard says a lot more Pfizer doses are needed to meet existing demand.

“The mixed messaging from the last six or eight months on the vaccines, particularly AstraZeneca, has not been helpful to the broader community’s understanding of how important it is to get vaccinated from any vaccine you’re eligible to get,” he says.

Concerns that current vaccines would not be effective against new variants have been allayed by research from the US Centers for Disease Control which shows that COVID-19 vaccines are still highly effective against hospitalisation despite the surge in the more transmissible Delta variant.

National Institute of Allergy and Infectious Diseases director Dr Anthony Fauci says as many people as possible need to be vaccinated now before more dangerous variants emerge.

“This is a very wily virus,” says Dr Fauci.

“If we keep lingering without getting those people vaccinated who should be vaccinated, this thing could linger on, leading to the development of another variant, which could complicate things.”

Were you thinking about holding off for a Pfizer shot instead of a second dose of AstraZeneca? Or have you already been double-dosed? Why not share your thoughts about the vaccines in the comments section below?

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