Early sensitive indicators of COVID-19 harm mitigation can detect vaccination impact in the New South Wales outbreak

 The Pundit has been searching for indicators that the New South Wales Covid-19 outbreak causing so much anguish in Sydney is at least turning the corner with moderation in health damage.

Gladys Berejiklian, the Premier of New South Wales,  has been repeatedly arguing that infection case numbers themselves are not the most important indicator of the status of the epidemic.

She definitely has a point. Most infections do not to cause obvious harm and it’s the minor fraction of patients with severe sit symptoms who are the main cause for worry. Metrics about the most severely threatened patients are clearly more important than total case numbers.

That’s what this post is about– measures of severe infection outcomes such as mortality and need to be admitted to an intensive care unit in an hospital.

These relevant numbers are available but only mortality figures are issued at press conferences each day and the form in which information about intensive care unit numbers are presented in recent press releases is not all that useful for answering the questions being considered in this post.

There are two types of epidemic control health interventions taking place in Sydney:

1. Limiting social interactions to prevent transmission and 
2. A rapidly accelerating vaccination campaign to improve immunity to bad COVID-19 disease.

Immunisation is currently giving around 66% first dose protection for eligible participants in New South Wales. This is enough to start having  a measurable effect over the coming days and weeks.

The frequent emphasis on epidemic case numbers is understandable, but case numbers themselves are not the most sensitive and early measure of vaccination impact.

Vaccination protection gives most effect to the most severe conditions, death, admission to intensive care units or hospitalisation. Protection by vaccines against infection, especially with infection by the Delta SARS CoV2 variant causing the Sydney outbreak is less dramatic than protection against severe outcomes of disease.

Fortunately there are obvious metrics for evaluating any impact on these severe health conditions from increasing levels of immune protection to the New South Wales population conferred by vaccination as time unfolds.

These useful metrics are deaths per week, new ICU admissions each week, and new hospitalisations each week.

The graphs below shows the progression of these parameters as compared with the increase in infection case numbers for the New South Wales outbreak.

The first graph deals with weekly deaths (orange bars) as a time series, with weekly new cases scaled by a factor of 100 also plotted (blue bars) to allow easier comparison of trends.

Trends in new ICU admissions each week are also available but they are not quite as extensive as mortality numbers.