(Image: ABACA Press/Robin Utrecht)

Australia is phasing out the AstraZeneca vaccine from September as those over 60 receive their second dose. It’s the vaccine we have in the highest quantities given it’s manufactured onshore — though it’s also the most contentious due to very rare links to blood clots.

Imports of Pfizer doses are expected to reach up to 1.3 million a week in September, and up to 2.3 million by December, while AstraZeneca doses will drop as low as 880,000 by September and given to states based on demand from December (though manufacturing will continue until company CSL fulfils its contract of 50 million doses, CSL tells Crikey).

Around the world, new research has shown mixing and matching vaccines might be the way to go. The UK still allows AstraZeneca for those aged under 40, and German Chancellor Angela Merkel received the Moderna vaccine two months after being given AstraZeneca.

Is the decision backed by science?

AstraZeneca was a free-for-all earlier in the year. By April the Australian Technical Advisory Group on Immunisation (ATAGI) advised those under 50 to have the Pfizer due to the risk of blood clots. Last week that was updated to those under 60 as more data emerged.

The risk of developing a blood clot is very rare, affecting an estimated 1.4 people between the ages of 60 and 69 for every 100,000 first doses. This increases to 3.1 for those under 50.

But every vaccine comes with risks — mRNA COVID-19 vaccines such as Pfizer and Moderna can cause anaphylaxis, a severe allergic reaction in 2.47 people in every 10,000 people. This morning the US Food and Drug Administration added a warning about rare cases of heart inflammation in adolescents and young adults for the same vaccines.

Sydney University infectious diseases expert Professor Robert Booy tells Crikey he thinks the decision to phase out AstraZeneca was only partially based on science.

“I do think it was influenced by public perception,” he said. “The risk is not just rare, but very rare, and the protection may well be better [from mixing vaccines].”

AstraZeneca was the wrong horse to back

The efficacy of AstraZeneca has been in question for some time, although data varies. Some evidence suggests it has the same efficacy as Pfizer, while new research suggests it may only be 60% effective against the new Delta variant (though this is still effective enough for the World Health Organization to approve a vaccine).

Professor of biostatistics at the University of South Australia Adrian Esterman tells Crikey Australia’s reliance on AstraZeneca wasn’t smart given the way the vaccine works always meant there was a risk of reduced efficacy.

AstraZeneca uses a chimpanzee adenovirus vaccine vector to carry the virus into the human body and generate an immune response.

“The trouble is that [when] the body responds to the vaccine, it can also respond to the virus,” Esterman said. “So when you get your second dose in some people it might not be as effective because the body is also responding to the adenovirus.”

Esterman said it was the wrong call for Australia to focus on AstraZeneca. Deals with Pfizer and Moderna came late, the local Queensland University vaccine was abandoned, and Novavax is still in clinical trials.

“There’s always a chance for any other vaccines that there might be safety issues or there might be effectiveness issues,” he said.

“Most of the countries have spread their bets and tried to get several … but unfortunately we only had one we could manufacture onshore.”

What will happen to excess doses?

About 6.8 million vaccine doses have been administered in Australia, most of which are AstraZeneca. CSL scored a contract to manufacture 50 million doses of AstraZeneca and has been manufacturing between 700,000 and 1 million doses a week. By December, the government plans to allocate doses based on demand — so what will happen to the remaining vaccines?

CSL tells Crikey it has no plans to pause manufacturing, saying it’s committed to meeting its contracted arrangements with the Australian government. The Health Department didn’t respond to Crikey’s questions by deadline.

Esterman and Booy say the excess doses should be donated — although donating vaccines our government didn’t want to give those under 60 isn’t a good look.

“We’ve used AstraZeneca for millions of Australians and it’s appropriate for us to also supply it to other countries,” Booy said.

“Kneejerk reactions of dumping of vaccines, just because perception is wrong, is not how we make decisions. We should make them based on science.”

Booy wants Australians to donate $10 to UNICEF after they have been immunised to provide a vaccine for a person in a poorer country through the global COVAX program.