Why five weeks extra vaccine rollout more than Sydney had made a huge difference blunting the severity of the Melbourne COVID-19 outbreak

Melbourne shopping at it's retail heaven peak.

Timing's everything.

The Pundit has searching for take home messages from the two major 2021 COVID-19 outbreaks in Australia.

Being stuck in the middle of a major outbreak and having strong protection from infection with the Astra-Zeneca vaccine makes him very curious about how vaccination played out quite differently in two cities that he dearly loves.

The marked difference in overall illness severity of the Sydney (New South Wales) and Melbourne (Victoria) outbreaks is very striking.

Although there were many more cases of diagnosed infection in Melbourne, hospital occupancy was much lower than Sydney:

Graph 1.

In puzzling through the differences, the Pundit spent time looking at the vaccine uptake profiles for the two Australian states displayed at https://covidbaseau.com/nsw/

and was stuck by how the COVID Base Au graphics display clearly shows marked differences between the states in extent of immune protection of the populace at the peak of the outbreaks.

The timing of these peaks is flagged as dates and coloured arrows in Graph 1 above.

Markedly better vaccine coverage of older people in Victoria at the outbreak peak.

Here is what he noticed by putting together the timing of these hospitalisation peaks shown in Graph 1 with the useful detailed displays of vaccination rollout progress displayed at COVID base Au, which are used as background in Graphs 2 and 3 below. The background graphs show full vaccination coverage as a percentage over rollout time in different age groups for the two Australian states.

Graph 2,

The large red arrow in Graph 2 represents the timing of peak New South Wales hospital occupancy noted in Graph 1 as happening near 15th September 2021.The dotted red arrow represents the range of full immune protection of the most vulnerable older groups, allowing for two weeks lag in protective immunity development. The numbers fall in a range which can be described as only giving partial protection -- that is near 50 percent of full immunity.

Here's a similar graph for Victoria ( Graph 3):

Graph 3.

As before, the large arrow indicates the timing of peak hospitalisation in Victorian outbreak against a background graph of vaccination delivery. The dotted arrow visualises the range of vaccine immunity delivered to vulnerable age-groups in Victoria, allowing for a lag in immunity development.

The main point emerging is that full protection of vulnerable age-groups was centred on 75 percent fully protected, substantially more than New South Wales' 50 percent.

As a cross-check, here is relevant double dose vaccine coverage for the key dates from the Federal government health agency:

Table added 27 Nov 21

Note how infection immunity protection for the older age groups listed that would kick in fully at the peak of the outbreak is substantially greater for Victoria than with New South Wales. These are people who are most liable to develop more severe disease and require hospitalisation if they get infected.

The Pundit reckons that these vaccination differences are enough to explain how Melbourne was much better off health wise than her sister city up north.

Five weeks extra vaccine rollout made a huge difference in overall health protection benefit.

It's called better protection of the vulnerable.

Updated 27 November 2021 with a data table.