Detecting impact of vaccination on COVID-19 mortality ratios during the New South Wales outbreak Part 1

In recent posts the Pundit has been exploring ways of detecting improvement to health outcomes during the New South Wales Covid-19 outbreak.

This effort gave an early signal of vaccination progress from hospitalisation ration numbers. 

Scrutiny of infection age profile changes over time gave a signal that over 50-year-olds may be benefiting from increasing vaccination rollout.

This post turns to grim statistics about death.  It’s purpose is to support appreciation of the value from rapid vaccine rollout

Apart from loss of life being a horrible situation for affected families and friends, mortality needs careful statistical interpretation to reveal meaningful guidance.

The Pundit is interested in finding out about the percentage of infected people who die from COVID-19, but detailed information to do this properly is not readily available. But relevant infection diagnosis numbers and death numbers are given each day in press conference reports.

We know that there is a lag between the time people get sick and the time of death, typically about 11 days.

We also know there is a lag between vaccination and the time when effective immunity is induced of about 14 days after the last vaccine dose.

A complication arises because two vaccine doses are needed for full immunity and there is partial protection from one dose of vaccine.

Putting these thoughts together, the Pundit came up with the following graphs of the situation in New South Wales.

First, a graph of  weekly numbers for mortality from locally contracted Covid-19 in New South Wales this year:

Sadly mortality continues to increase. The numbers themselves give no obvious indication of improvement in outcomes, and  in the early weeks 27 through 30 there are low numbers which are likely to be imprecise metrics by themselves. By the end of the period, COVID-19 mortality numbers are large each week and so weekly numbers themselves should be a meaningful metric .

From this mortality information, and recorded numbers of diagnosed COVID-19 infections mortality ratios were calculated at the end of each week and are presented in the next graphic:

This graphic uses for calculations the cumulative number for mortality  up to the end of the week recorded on the horizontal scale. The crude case fatality ratio (CFR) represents cumulative numbers of cases and deaths for the same week. As there is a lag between getting ill and passing away, a lag adjusted case fatality ratio based on the average of the cumulative case for the 2 prior weeks to the week in which death occurred as a denominator was also calculated.