Key message: Vaccines act two ways to decrease mortality from COVID-19 : they decrease both the chance of infection and -- as demonstrated here -- the chance of death if you get infected.
Updated 2-Oct-2021, 6-Oct-2021.
This post continues a theme investigating COVID-19 harm reduction in the major Australian population centres -- Sydney and Melbourne.
These cities are in the middle of rapid vaccine rollouts in the midst of surging coronavirus infection numbers.
Portugal have been there already, with their marvellous progress highlighted in the Financial Times 28 September 2021 by Peter Wise.
Portugal emerges as Europe’s vaccination frontrunner after public health drive
A former submarine commander has instilled confidence in jab programme that had a faltering start
Here are graphical summaries of what has happened in Portugal from the superb Our World in Data website:
After the first moderate wave of cases in March-April 2020 there was a large surge in winter 2020-21, followed by a smaller surge in cases in the late summer of 2021, that slowed as the vaccination coverage became substantially complete in mid-September 2021.
The effect of vaccination rollout is best seen from daily case numbers and double dose vaccination percentages in this graph:
Effects of vaccine on disease severity
Deaths are one measure of the severity of these waves of infections:
The graph show the mortality impact of the Portuguese winter 2020-21 case surge was awful, with around 14,000 people losing their lives. But the late summer infection wave impact on loss of life was relatively marginal.
This means that infection fatality ratios (deaths per 100 infections) changed significantly for the better between these waves.
A direct way of calculating how deaths per 100 infections changes is to examine the relationship between deaths and case numbers in a graph. The infection fatality ratio is directly related to the slope of lines in such a graph.
For the Portugal outbreaks using numbers for cumulative deaths and cumulative cases from Our World in Data, we get this graph:
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| 11 day lag adjustment applied to deaths Black arrow indicates onset of fully protected immunisation |
The most distinctive feature of this graph is the change in slope just after 800,000 cases, indicating a dramatic drop in mortality per 100 infections .
The slope between 400,000 cases and 600,000 cases gives a death rate of 2.54 deaths per 100 infections.
The slope from 900,000 cases to 1,060,000 cases is 0.46 deaths per 100 infections
(This compare with fatality rates of 0.7 percent in the Sydney 2021 outbreak and 0.51 in Melbourne Delta 2 outbreak)
Its useful to also check the rollout of full vaccination coverage in Portugal:
Total deaths are affected by both fatality rates and total infection numbers, and low infection numbers are crucial for reducing harm.
Update 1900 hrs 30 Sept 2021
Our World in Data provide information on weekly hospitalisation in Portugal. This enables examination of whether vaccination has an effect on rates of entry into hospital of people given a COVID-19 diagnosis:
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| Black arrow indicates a point in the curve where a change of slope indicates decreased rates of hospitalisation from COVID-19 |
Examination of the slopes shows that after the point indicated by the black arrow, rates of hospitalisation of infected persons were 2.8 fold lower. At this point vaccination fully effective coverage was above 30 percent.
Australia should be reaping these extra benefits from vaccines already.
Equivalent approximate 30 percent full immunity coverage is expected to have occurred around 12 September 2021 in New South Wales and 16 September in Victoria. Hopefully both Australian states are getting further respite in terms of hospital case load from this source of damage mitigation relief that reduces the proportion of infected people needing to go the hospital.
This graph below taken from an earlier GMO Pundit post shows the time series of weekly hospitalisation ratios to cases in New South Wales. A black arrow indicates the approximate time at which full suppression of disease severity by vaccines is expected to kick in.
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| Week 36 ends 11 September 2021 |
Looks to the Pundit that vaccines arrived in the nick of time to mitigate some disease severity in Sydney. And if indeed we get 15 percent necessary hospitalisation rates even with substantial vaccine softening of disease severity, it definitely means that the COVID delta variant disease is a truly nasty beast.
Afternote 1 Oct 2021
The harmfulness of the Delta variant in Sydney was more extensively discussed in an August 27 2021 GMO Pundit Post:
A very recent pre-print publication from Washington state further confirms some of the vaccine benefits noted in these posts.
It has an instructive diagram showing difference in risks as ratios:
This is further evidence that the SARS-CoV2 delta variant strain has increased virulence that increases the need for patient hospitalisation above that of early pandemic strains.
Preprint: Associations between SARS-CoV-2 variants and risk of COVID-19 hospitalization among confirmed cases in Washington State: a retrospective cohort study
Interpretation: Infection with a Variant of Concern [including Delta] results in a higher hospitalization risk, with an active vaccination attenuating that risk. Our findings support promoting hospital preparedness, vaccination, and robust genomic surveillance.
https://www.medrxiv.org/content/10.1101/2021.09.29.21264272v1.full.pdf
Update 11 Jan 2022
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