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Pharmaceutical companies Pfizer and BioNTech have announced their COVID-19 vaccine is effective in preventing the virus in 90% of participants. 

This number is huge — flu vaccines are only 40% to 60% effective — and the news sent stocks soaring. 

But experts have warned the data has not yet been peer-reviewed, stressing cautious optimism is needed and maintaining social measures are important to prevent the virus from spreading. 

Cause for cautious optimism 

The phase three study recruited 43,538 participants who received either the vaccine — administered in two shots about three weeks apart — or a placebo alternative such as the meningitis vaccine. 

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There were 94 confirmed COVID-19 infections among the participants. Pfizer hasn’t released the breakdown of those cases, but the 90% efficacy rate means most people who caught it had been given the placebo vaccine. No serious side effects have been reported. 

Australian National University infectious disease specialist Associate Professor Sanjaya Senanayake told Crikey the results were incredibly promising. 

“If it holds up, it’s very effective, it’s very good, and it’s unexpected … and there’s no reason to suspect this number won’t hold up,” he says. 

But this is based off an initial report. Pzifer hasn’t yet released its full analysis or the data for peer review. 

First of a kind with many unknowns

There is still a lot we need to know about the vaccine: how long it is effective for; how effective it is in vulnerable populations; how it will be manufactured and distributed.

Both Pzfier and Moderna are developing an mRNA vaccine, releasing the bare bones genetic code into the body instead of using part of the virus’s body. AstraZeneca’s vaccine uses a viral vector — the skeleton of a virus as a host. 

If successful, these will be the first commercially viable mRNA vaccines in history.

Kirby Institute immunovirology Associate Professor Dr Stuart Turville said the benefit was that they were easier to manufacture than viral vector vaccines. The bad news was they have to be stored at -70C, a worrying factor for countries with limited cold storage facilities.

“For scalability, it’s a lot easier,” he said. “Making a viral vector is a lot more involved in the context of production.” 

But Australia has viral vector manufacturing capabilities, he said.

Yesterday, biotechnology company CSL started manufacturing the AstraZeneca vaccine in two facilities in Melbourne. 

“The manufacturing powerhouse in Australia has always been seen as a strategic leverage,” Turville said.

AstraZeneca hopes to release its data before the end of the year. 

We also don’t know how it holds up to mutated versions of the virus — including a worrying strain found in minks. 

“With 40 million infections the virus has changed and there are a number of flavours,” Turville said. “Subtle changes in the virus might make it more resistant, and it might take the edge of this vaccine.” 

Don’t throw caution to the wind 

Don’t celebrate until the data has been properly scrutinised, said David Henry, professor at Bond University’s Institute for Evidence-Based Healthcare.

“We’ve learnt in the pandemic the risks of prematurely celebrating results,” he said. “We saw what happened with hydroxychloroquine,” where results from small trials overstated the efficacy of the antimalarial drug. 

“We need to look at the quality of the study … and the statistical precision of the data.”

With nearly 44,000 participants, Henry said the control infection rate of 94 was incredibly low — just a fraction of a per cent. 

“There is statistical uncertainty,” he said. Not knowing how long the vaccine lasts is another concern: “Infections will accrue over time and the infection rates in the two groups may start to close if immunity wears off.”