There may be confusion over vaccines after the Australian and New Zealand Society for Immunology published its opinion earlier in the week and then changed it within hours.
The umbrella body for vaccine experts said that the federal government should pause the planned rollout of its favoured AstraZeneca vaccine because it may not be effective enough.
The phase three trial of the vaccine developed by AstraZeneca and the University of Oxford showed it to be 62 per cent effective in preventing COVID-19 compared with 95 per cent for the approved vaccines made by Pfizer and by Moderna.
So where do we stand?
First, some terms
Efficacy is measured by how many vaccinated people in a hundred get the disease, so 95 per cent efficacy means the vaccine works for everybody but the five per cent.
Technically speaking "efficacy" and "effectiveness" aren't quite the same. The first measures how many vaccinated people don't get the disease in the trial and the second term measures how many don't get the disease in real life once the vaccine is in general use.
Trials depend on volunteers and a 100-year-old person, for example, is unlikely to volunteer so the trial doesn't quite get a cross-section of the population. Either way, 95 per cent effective is very effective.
Herd immunity is where so many people in a population are immune from getting the disease that the chances of catching it are very low.
An important note: the vaccines approved so far stop people getting ill from the virus but not from being infected by it. They stop the symptoms (which means you don't get sick or die) but they don't stop you actually catching the virus (which means you may still infect other people).
With the three main vaccines, the trials tested whether people actually got ill (developed symptoms) and not whether they caught the illness without symptoms. None of the manufacturers and researchers have given figures for immunity from being infected because it's too early to know.
The vaccine developed by AstraZeneca and the University of Oxford is the only one which will be manufactured in Australia, but it is less effective than the alternative Moderna and Pfizer vaccines.
The government says:
- Australia has secured 53.8 million doses of AstraZeneca vaccine;
- 3.8 million doses will be delivered to Australia in early 2021;
- 50 million doses will be manufactured in Australia in monthly batches. CSL will manufacture these doses on behalf of AstraZeneca.
The government has ordered 10 million doses of the vaccine from Pfizer and the BioNTech researchers, to be available from early 2021.
But since the population of Australia is 25 million and each person needs two doses, 10 million doses would leave 20 million Australians unvaccinated.
So what's to be done
Should we just order more of the more effective vaccines?
It's not as simple as that because their supply is limited. We are competing with the rest of the world, including the United States where the companies are based.
But the AstraZeneca vaccine still promises to be pretty effective when its full results are known. The doubt over it is because there was a glitch in the trial. By accident, only a half dose was given to some volunteers but this turned out to be more effective than the full dose. A full, robust analysis of its effectiveness is awaited.
The country's chief medical officer says that we work with what we have. "The choice is not whether one is better than the other, it's which one is available to give the maximum rollout of vaccine to save lives and to protect lives this year," Paul Kelly said.
Epidemiologist Adrian Esterman, a professor at the University of South Australia, told this paper that he favoured vaccinating the vulnerable as soon as possible with the Pfizer vaccine, and then holding off until March or April when we should know more about the AstraZeneca vaccine which is being produced in Melbourne.
"If, after the full phase-three trial results are in, the AstraZeneca efficacy remains close to 60 per cent, then it would not be possible to achieve herd immunity using this vaccine,' he said.
The AstraZeneca vaccine may be less effective but it is much cheaper. Professor Esterman believes that cost should not be a factor in which vaccine we use because the cost of a lockdown would be so much higher.
The more expensive Pfizer vaccine costs $20 a dose - $40 for the two doses each person needs - and that adds up to a billion dollars ($1,000 million). This, though, is chicken feed compared with the cost to the economy of a continued epidemic.
"It's nothing compared to three days of lockdown," he said.
What about mixing and matching?
Nobody quite knows whether using a mixture of, say, the Pfizer vaccine and the AstraZeneca one on the same person would work but health authorities aren't keen.
"We do not recommend mixing the COVID-19 vaccines," Dr Mary Ramsay of Public Health England said. "If your first dose is the Pfizer vaccine you should not be given the AstraZeneca vaccine for your second dose and vice versa."
She did concede that there may be "extremely rare occasions" where, for example, which vaccine the patient received for their first dose wasn't known.
"Every effort should be made to give them the same vaccine, but where this is not possible it is better to give a second dose of another vaccine than not at all," she said.