Fudging the Figures

Much is being made of the fact that Australia has reached 80% first dose vaccinated for covid19. And look, that’s wonderful. But it’s also a bit of a lie. We are not 80% first dose vaccinated. We are 80% of people over 16 first dose vaccinated. As a percentage of the whole population, we are at 65% first dose vaccinated (according to figures I found here, and using the ABS estimate of Australian population of 25,704,340 as at March 2021).

Until recently, vaccination coverage, especially in the context of herd immunity, was reported as a percentage of the total population. That makes sense, because when we’re thinking about herd immunity, we want to know how many people are vaccinated, not how many people over 16. The virus doesn’t stop to check your age before it infects you, or before it gets you to spread it.

Different viruses require different levels of vaccination to achieve what we call herd immunity. For example, according to the WHO herd immunity for the measles is achieved at 95% vaccinated, whereas herd immunity for polio only requires 80% vaccinated. This is probably because different viruses spread in different ways, and have different levels of infectiousness. We’ve seen that with the Delta variant of covid19, which spreads much more easily than the earlier variants of covid.

For our purposes, a useful definition of “herd immunity” is: “enough people are immune to the virus that it no longer causes widespread societal disruption” – such as overloading the health system, and making a lot of people very, very ill. Herd immunity doesn’t eradicate a virus, but it means enough people are immune that the virus is not going to spread unchecked through the population.

The trouble is, we don’t know what level of vaccination we need to achieve herd immunity for covid19, because it’s too new – we simply don’t have the data. But everything we do know about the virus suggests we’re going to need a high level of vaccination, rather than a lower one. And herd immunity is always calculated as a percentage of the total population.

Currently, in Australia, everyone from 12 years and upwards is eligible to be vaccinated. This makes it particularly bizarre to report vaccination percentage relative to 16 years and older. It’s nonsensical. It’s not relevant to herd immunity, not is it relevant to the people currently eligible to be vaccinated. At the very least, we should be reporting as a percentage of the population 12 years and older.

In Australia we currently have 3,825,589 children under 12 – that’s 14.9% of the total population. We know that age makes no difference to ability to catch & spread the virus (despite much shrieking by right wing loons to the contrary), though it does seem to make a difference to average severity – no consolation to those young people who were not average and died, or who suffer long covid still.

Epidemiologists calculating herd immunity use total population – remember that the virus doesn’t check your age before deciding to infect you, or to have you spread it – so, in reality, we need to know the percentage of the total population that’s vaccinated.

The current percentage of the Australian population that’s double vaccinated according to the Sydney Morning Herald is 49.15%. The SMH site is useful because you can toggle between eligible population and total. Because the vaccine is not yet approved for kids under 12, they can’t yet be vaccinated. You could argue, therefore, that it’s only the eligible population we’re interested in.

Sadly, the virus is interested in all of us, regardless of eligibility. That makes the percentage of the total population vaccinated crucially important.

And here’s the thing. The Australian Federal Government, which has pushed all along for living with the virus, for no lockdowns, and for the economy over lives, has decided that 80% of the adult population being vaccinated is quite enough to go back to business as usual. Open borders, international travel, let’s get this rubbish behind us and pretend it never happened. (Actually, further investigation reveals that another document says 80% of the 16+ population. It was released by the Prime Minister’s office on the same day as the one that says 80% of the adult population. It’s actually an attachment at the bottom of that same page. It makes accurate calculations and comparisons rather difficult.)

The total Australian population over 16 is 20,619,959. 80% of that is 16,495,967.2. Note that we’re not even considering the eligible population here (12+). Just the population aged 16 and over. 80% of that population vaccinated amounts to just 64% of the total population. Nowhere near enough for herd immunity.

How about some pie charts? Everybody loves a pie chart, right? Which pie chart makes it look like our vaccination numbers are better? Note these pie charts all show exactly the same vaccination data. Just using different slices of the population to compare against.

Pie chart of vaccination rates reported against total population. Slightly less than half (49.5%) are double vaxxed, a little over a quarter unvaxxed (31.8), and the remaining (18.7%) single vaxxed.
Percentage of total population vaccinated
Pie chart of vaccination rates reported against 12+ population. More than half (58.1%) are double vaxxed, a little under a quarter unvaxxed (19.9%), and the remaining (21.9%) single vaxxed.
Percentage of 12+ population vaccinated
Pie chart of vaccination rates reported against 16+ population. More than half (61.2%) are double vaxxed, a little under a quarter unvaxxed (18.1%), and the remaining (20.7%) single vaxxed.
Percentage of 16+ population vaccinated

The best of the bunch, if you want to make the vaccination rates look better, is the graph for 16+. And our government’s target of 80% double vaxxed doesn’t sound nearly as good when you know it’s only 64% of the total population. Nowhere near any plausible estimate of the numbers we need for herd immunity.

Sadly, the covid19 virus can’t read graphs, and is not interested in massaging the numbers until they make you feel good. It wants to infect as many people as possible. Fooling ourselves – or allowing ourselves to be fooled – only makes that easier.

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