Extensively revised 16 09 2021;Revised 17 09 2021 Updated 24 09 2021, 4 10 2021, 24 10 2121 with more data
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. Records of hospitalisations during this outbreak in NSW government reports clearly show higher likelihood of hospitalisation with older people if they get infected, as compared to what happens when the young are infected. Older people were understandably given priority in the vaccination queue and have higher levels of vaccination acceptance in the early stages of the outbreak than the young.
This post extends an earlier post where the Pundit pondered a possible light at the end of the nasty New South Wales 2021 COVID-19 tunnel: Predictable trend of improvement in the odds of staying out of hospital in Sydney
The silver lining in Sydney: Successful mitigation of damage. Let's move on.
New South Wales weekly COVID-19 surveillance report are fascinating and detailed lockdown reading, but many readers may like a shorter version of their findings.
The following graph is an updated and simplified version, made by the Pundit, of similar graphs appearing in recent NSW government weekly reports for week 32 to 34 of the epidemiology year.
 |
| Differences in bar height between paired bars indicate different rates of disease transmission. Sydney grandparents have been shielded. The young much more exposed to infection. |
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 each 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 effectively protected from infection during this outbreak. Similar protection is seen for ages 50 to 69.
Another way of presenting this is to calculate relative risks of infection for each age group, as shown here:
This pattern shows public health interventions, vaccination and social distancing, have succeeded in preventing many infections in vulnerable people 50 and over during this outbreak.
Marvellous news this is, and a fine public health achievement, despite its imperfect implementation and failure to halt transmission. It is a very different story to COVID-19 in Australia in 2020.
Another 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 for these ages.
Elsewhere in the news 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.
 |
| Arrows indicate age-groups whose numbers are increasing as a fraction of total cases |
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. This decrease may be contributing towards lower rates of hospitalisation as this age-group are susceptible to severe disease. The elderly maintained 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. (Perhaps they are parents with young children and need to take them to school, increasing their risk of infection?).
These features of infections highlight 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.
The message for Victoria is the same as ever. Learn from Sydney's hard yards.
Go out and get vaccinated -- especially if you are 20-something-- because it works, is really good for the whole community, and is the only way out of this mess.
Data Source: NSW COVID-19 cases by age range
Update 24 Oct 2021
More data has become available, so the last figure has been extended with age classification of many further COVID-19 diagnosed people for more recent periods through 23 October.
Here is the graph:
The profile is essentially the same as for the immediately previous period analysed except for the age-group 0-19 and 20-29 years.
There has been a steady increase in proportion of the youngest age-group getting infected. These are the least vaccinated group.
The 20-somethings are a steadily declining fraction of cases, suggesting that they are being increasingly sheltered from infection by immunisation. (They started the outbreak with low coverage of vaccine protection. On 17 July for example, less than 12 percent of under 30 year-olds had even one dose of vaccine.) There are no further increases in proportions of 40 to 59 year-old getting infected. The Pundit suggests that the benefits of expanded age coverage for immunisation are now being seen in ages 20 through to 59.
See also a later post:
No comments:
Post a Comment