Explainer: Moderna COVID vaccine approved in Australia

The COVID-19 vaccine made by American company Moderna has been given provisional approval in Australia by the Therapeutic Goods Administration.

The Federal government has ordered 25 million doses of the Moderna vaccine, 10 million of which will arrive in 2021, beginning next month. The other 15 million will arrive in the first half of 2022.

How does the vaccine work, what’s in it, how good is it at preventing COVID, and does it have any side effects? Read on to find out.

How does the Moderna COVID vaccine work?

The Moderna vaccine is a two-dose mRNA vaccine, very similar to the Pfizer vaccine. It works by adding messenger RNA to our cells, which the body uses to make coronavirus spike proteins (but not the rest of the virus).

Paul Griffin, an associate professor of medicine at the University of Queensland, says that the Moderna vaccine is “similar to Pfizer in terms of mechanism of action, safety, efficacy and effectiveness.

“Subtle differences include that the interval is four weeks between doses for Moderna, as opposed to three typically with Pfizer, and it does appear Moderna has slightly more temperature stability data so is a little easier to transport and store.”

How effective is it?

In US-based Phase 3 trials last year, the vaccine had an efficacy of 94% at preventing COVID-19 infection, and 100% at preventing severe disease. Clinical trials in other parts of the world have produced slightly different numbers.

Because there are differences between clinical trials, it’s not a great idea to compare absolute numbers from Moderna to those from Pfizer, AstraZeneca, or any other vaccine. An efficacy of 94% doesn’t mean that the vaccine is definitely better than one with an efficacy of 90%.

Professor Adrian Esterman, chair of biostatistics at the University of South Australia, says the Moderna vaccine is likely to be effective against the Delta variant of COVID-19.

“With respect to the Delta variant, the Pfizer vaccine has an efficacy of 88% at preventing symptomatic COVID infection after two doses and is 96% effective against severe disease or death,” he says.

“It is expected that the Moderna vaccine will have similar efficacy.”

You should talk to your GP or healthcare provider about your personal situation, but in general, the best vaccine for you is the one that’s available to you.

What’s in it?

The Moderna vaccine contains:

  • Messenger ribonucleic acid (mRNA), which is the active ingredient that triggers our immune system
  • Lipids, which coat the mRNA so that it can get into our cells
  • Salts and bases, which keep the pH of the vaccine stable
  • Sugar, or sucrose, which keeps the mixture stable
  • Water, which mixes all the other ingredients together.

If you’re keen for more details, we’ve covered vaccine ingredients for all approved Australian vaccines in this article.

“Interestingly, a dose of Pfizer contains 0.3 millilitres of vaccine, whereas Moderna uses a dose of 0.5 millilitres – yet they have the same efficacy,” says Esterman.

There’s some evidence that a quarter dose of Moderna might be enough to prevent severe COVID. Using it this way would dramatically increase supply of the vaccine.

Are there any side effects?

As with the other approved vaccines in Australia, the Moderna vaccine can produce mild side effects immediately after administration, including pain and swelling at the injection site, tiredness, headache, fever and muscle pain.

“The side-effect profile of [Moderna and Pfizer] is very similar, and any side effects usually occur after the second dose,” says Esterman. This is in contrast to the AstraZeneca vaccine, which usually has more severe side effects after the first dose.

As with all vaccines, there have been occasional reports of other more severe reactions that might be linked to the vaccine (such as this single case study of an already-ill patient who developed blood clots). Even if they are linked, these side effects are extremely rare, and the vaccine carries a much lower risk than that of contracting COVID.

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