Age-shifts in burden of infection are helping to soften the damage to health in NSW from COVID-19 Delta variant

Extensively revised 16 09 2021

This post explores the age distribution of COVID-19 infections in the current New South Wales as a possible factor influencing a decrease of proportion of serious disease. Data of hospitalisations during this outbreak in NSW government reports clearly show higher likelihood of hospitalisation with older people. Older people were given priority in the vaccination queue and have higher levels of vaccination acceptance.

This post extends an earlier post the Pundit pondered a possible light at the end of the nasty New South Wales 2021 COVID-19 tunnel: Steady predictable trend of improvement in the odds of staying out of hospital in Sydney

New South Wales weekly COVID-19 surveillance report are fascinating lockdown reading but many readings may like a shorter version of their findings. The following graph is an updated version by the Pundit of similar graphs appearing in recent NSW government weekly reports for week 32 to 34 of the epidemiology year.

The blue bars are the proportion (as a percentage)of all infection for each of the age-groups mentioned. The orange bars are analogous proportions (percentages) for the total state population. These allow assessment of the degree of protection of the age-group from infection during the outbreak.

The blue bar for Age 70+ is much less than the orange bar for that age-group, indicating that the elderly have been very effective protect from infection during this outbreak. Similar protection is seen for ages 50 to 69.

This pattern shown public health interventions, vaccination and social distancing, have succeeded in preventing many infections in vulnerable people during this outbreak.

This is marvellous news.

The other main message from this graph is that the young are carrying most of the burden of infection.

30 percent of infections are in people under 20. All ages under 39 carry more infection than expected from population numbers in these ages.

There are encouraging signs that this burden could be lifted with younger ages now getting access to vaccines and taking up the opportunities for becoming immunised in increasing numbers.

How are age-profiles of COVID-19 infection changing over time?

The Pundit started this line of investigation to see if changes to the age distribution of infection during the NSW outbreak could indicate a reason for decreasing rates of hospitalisation in SARS-CoV2 infected people.

Here is a graph that examines this, by comparing the infection profiles in the most recent few weeks (September) with those at the start (early July) of this outbreak.

The 50-something year olds are a decreasing proportion of total cases in the last few weeks. This may reflect increasing vaccine take-up in this age-group. The elderly maintain good levels of protection against infection throughout the outbreak.

The black arrows indicate age-groups that are making up an increasing fraction of infections.

These are middle aged people who need to be aware of this risky trend, and make sure they take more aggressive steps to minimise harm to themselves from COVID-19.

Both these findings  highlights the importance of encouraging and supporting the participation of all age-groups in immunisation programs.

They also indicate conversations about vaccines with younger people — who carry most of the infections — may hold the key to taming these Australian outbreaks

Hopefully we will continue to see weekly infection numbers in NSW coming down too.