COVID-19 mortality rates improved in Victoria coinciding with SARS-2 Omicron but weeks of deaths are already locked in

Huge numbers of infections have been a serious worry in Melbourne Australia since the Omicron variant epidemic wave burst into activity late December 2021. High patient numbers are challenge for the hospital system.

Amid this crisis some encouraging epidemic news has been understandably largely side-lined.

Death rates (lives lost be 100 infection have dropped). 

Perhaps the reason is that interpretation of these matters is tricky, and it is bitter sweet news. It’s easy to underestimate these rates. One reason is that deaths lag the onset of illness, and in a rapidly expanding outbreak this lag has to be accounted for.

Pundit think is best to get this news out.

In the absence of detailed patient records, here is one approach to finding out what’s happening. 

First the time course of cases and deaths are as follows:

In this graph, daily case numbers in blue have been scaled by multiplying by 0.59/100 to align with the numbers of lives lost per day

This multiplier accurately predict the level of death following infection during the October-November Delta variant wave, but there is a lag of death number behind infection numbers.

In the New Year, infection numbers took off like a rocket– this is largely Omicron variant.

But daily lives lost, thankfully not so much of a surge, but there was a lag before they indeed did rise too.

The make more sense of these we need to look at cumulative numbers.

Here they are for infections numbers against date of announcement

These first wave in this period amounted to some 100,000 cases and was caused by the Delta variant of coronavirus. Omicron variant was detected when there were about 100,000 cumulative cases but there was a lag before it dramatically influenced case number counts. Bear this profile in mind when considering the next graph.

Deaths plotted against cases enables visualisation of the severity of mortality.

The graph below plots the cumulative number of deaths versus the cumulative number of infections 11 days earlier, when on average these people would have first suffered symptoms and been identified. (NSW Health Service provide this estimate in their weekly reports on COVID-19.)

The first part of this graph has a constant slope. This is the time of the Delta wave of the Victorian  COVID-19 epidemic.

The constant slope indicate very sadly that 5.9 people died in every 1000 detected infections.

Remarkable the slope changed about the time in the epidemic that Omicron variant started to circulate.

This softens the blow of the epidemic a bit. 

We thus from the slop of the graph, can expect at the moment about 3 or fewer deaths per 1000 Omicron variant infections.

The Lag is a killer.

But further rises in deaths will surely come. We already know the daily case numbers that will produce those deaths, and daily deaths are likely to average near 30 lives a day over the next two weeks.

But if daily infections moderate the next few day, there will be respite around three weeks ahead.

That’s the reality of an 11-day lag.