Influenza (flu) cases have been rising rapidly in Australia this year. Some see this as a result of waning immunity during our border closures. Some see this as the harbinger of a big northern hemisphere winter flu season. I think it’s simpler than that. But let’s step through a few things to see if flu is on the rise early in Australia.
Is the flu season looking like anything special?
Yes, Take a look at the graph below from our combined national flu data. We can see what looks like two things from this graph.
- This looks like a very steep rise in flu positive lab tests
- This rise looks earlier than we normally see
But is it real or – as we seem to ask every year – “is it just because of more testing”?
The quick answer is – this alone doesn’t tell us. I can tell you that Australia stepped up its laboratory capacity to cope with SARS-CoV-2 pandemic testing and a lot of those analysers and equipment can be switched over to flu virus testing – or more likely, flu+SARS-CoV-2 (and sometimes +RSV) testing. So these flu numbers will be higher than they would have been pre-pandemic. But is testing so much higher that we can discount the shape and timing of the steep rise in 2022?
No, not in my opinion and I’ll show you why I think that next.
But first – remember the flu viruses?
Those good old days when disease and virus names were similar?
But if you’d like to know a bit more about these viruses – I have a few other older blog posts that might still help.
- An influenza virus is the sum of its parts
- Flu, genes, clades and H3N2
- Which is the inFLUencing hemisphere, north, south or neither?
- Every flu season is a soup of viruses
- Influenza seasons are unpredictable: deal with it
- Influenza virus transmission: with or without symptoms, you’re dropping Flu virus
Apart from positive test numbers, is there any way to be sure it’s truly flu season?
Why yes me, and thank me for asking.
The number of positives per total samples tested
This is an essential figure. This proportion, expressed as a percentage, requires that we divide the number of flu positives by the total number of tests done. Despite being so simple, a graph of these data is often missing from Australia’s jurisdictional reports. Why? 🤷
But it is included in the national report.
An even better way to view this proportion if comparing between different places is to express it as the number of positives per 100,000 population. That way we can see how Brisbane compares to Baltimore (does Baltimore have a report that does this? Well, it does, but it’s not up to date would you look at that (click on the Clinical Labs tab).
But back to Australia though. For some context let’s look at the same graph for 2017 and 2019 which were both definitely #flunami years here. We can see that the infection rates per 100,000 were higher at the same time in 2019, and lower in 2017 than they currently are at the end of autumn 2022.
If you look at that first graph above, you’ll note that 2017 was a big but late starter season while 2019 was a big but early starter season. So we’re on track for something different again – steeper, earlier. It will be interesting to see how this progresses during winter.
If we just look at the rate of laboratory positivity in sentinel labs, it’s moving up, so again there is a change happening.
And across all of Australia’s disparate testing locations, cases really have jumped up in a short period of time. It’s not hard to see why our child and adult hospitals and workplaces are straining under the weight of a flu epidemic on top of a SAR-CoV-2 epidemic alongside epidemics of other respiratory viruses.
This is definitely an early flu season as the per population and lab positivity are realistically above baseline. So while test positivity rates aren’t as high as in the same period in 2019 they are higher than in the same period in 2017.
Flu-positive people who are sick enough to be admitted to hospital
This is another marker of flu activity that is above baseline. Hospitalisation & ICU numbers are almost identical to 2019 but above 2017. And they are above what happens outside of “flu season”.
The last fortnightly flu report (a new one due out later this week) noted 3 lab-confirmed influenza deaths so far in 2022 (+3 since the previous fortnight).
Among sentinel hospitals, there had been 368 admissions during that same period (+215 from the preceding fortnight). Of those admitted to a hospital, 28 (7.6%) went into an intensive care unit (ICU; +21).
What is the main virus driving the Australian flu season right now?
It’s all about a FluA strain called H3N2 and its variants. This virus has been a growing thorn in everyone’s side and so it wasn’t shocking to see it be the first one to charge back.
As best I can tell from NEXTSTRAIN – theres’ not a lot of Aussie flu sequences easily visible – these are variants of the 3C.2a1b.2a.2 clade, which has been the most active recent clade. There are also very similar viruses isolated from what looks to be earlier from, for example, the US. Interestingly, the US flu season is also dragging on.
Flu “doesn’t just come from the ground”
..to paraphrase Dr Norman Swan from a couple of weeks ago.
Viruses need to either be constantly ticking over (endemic viruses like RSV, rhinoviruses, adenoviruses) or introduced via zoonosis or travel. We saw the obliteration of the 2020 and 2021 flu season because we prevented infected travellers from entering Australia via travel restrictions and the use of quarantine at the border.
Turns out, flu needs new variants to be introduced for it to create a “season”.
In 2020 almost all (20,158 of 21,266; 95%) lab-confirmed flu notifications reported up until the end of October, occurred before April 19th, then flu fell off a cliff. That date is a month after the March 20th national border closures and soon after we locked down our internal borders.
In 2021 – up to November – Australia reported just under 600 cases for the entire year. Hundreds of flu-related deaths were prevented. Probably more since we’re unlikely to be capturing the longer-term impact of flu damage on the cardiovascular system.
So the current Australian season may indicate yours is about to be big. Or it may not. Or it may have been going to be a huge one anyway. Or your next season may be due to another flu strain entirely given that it looks like ours was seeded from your winter just past (cheers).
Always hard to predict. The northern hemisphere may get all these slightly Aussie modified viruses back and there might be a big winter of SARS-CoV2 and influenza virus stress for those healthcare systems. That is what we are in the midst of here and it is only just the start of our winter (it starts in June).
It would be a good idea for hospitals and aged care and places of work to be planning ahead for a big winter of respiratory viruses. Because we don’t just have the two concurrent plagues, we are also seeing a rapid increase in RSV, adenoviruses, rhinoviruses, enteroviruses – the gang’s all here.
One super-important, can’t be said often enough aspect of such planning is educational communication. In the many countries with a vocal, angry mask-hating community, start planning big educational campaigns that explain why to wear a mask, where to wear a mask, what masks to wear, when to wear a mask and how to wear a mask. Masks reduce risk to you and others.
Also, prepare for a decent wave of bronchiolitis if you have been a country using stay-at-home orders to help save your lives in your community.
And with RSV levels so high it’s unsurprising that bronchiolitis (“RSV is the most common cause…” sic *any* textbook) presentations are up from 387 to 442 this week in children aged 0-4 years; 41% admitted to hospital. Bring on that damn vaccine!
Another is to talk about flu vaccination. Vaccine fatigue is real so it’s likely you don’t have good flu vaccine coverage in your community. Without that, flu is going to put more people in hospitals than it would with more vaccine coverage. And don’t bother with R0 comparisons. Who cares? The fact is that respiratory viruses all transmit bloody well through the air and that’s all you need to know.
Another is to think about air quality. Our health relies on pure water and safe food. We feel better surrounded by clean surfaces. We need to get it into our heads to expect clean air – pathogen-free air or at the very least a lower load of pathogens in the air we inhale. There’s lots of space for innovation here.
But flu won’t be a problem until winter, right?
Probably. But we’ve seen enough evidence now that if the virus is novel enough, it’s our stupid behaviours that drive its spread not the season. You haven’t; seen that? Then why are you reading this? Go away! If we all huddle together because it’s cold (as per a northern winter) then the virus will take advantage of proximity and stale air and it/they spread.
And remember, the tropics support flu virus replication (and mutation) all year-’round. It’s not flu viruses that like the seasonal changes. It’s our response to them that gives them the chance to thrive. Australia’s east coast flu season took off before the normal start period, while it was still relatively warm and human and flooding. The rains likely played a role in keeping us indoors as well. Behaviour people.
What can I do?
- Get a flu vaccine. Get your COVID-19 3rd dose (remember when we cared about hospitals and healthcare workers and didn’t want to overwhelm the system??)
- Wear a well-fitting P2/N95 mask (so you can’t smell cigarette smoke when wearing it)
- Be on the lookout for stale air and stay clear!
- Think about what you’re doing snd what you want – if you don’t care about getting infected, cool. If you do, maybe put off that indoor restaurant meal and eat outside instead?