Flu Season 'Early Spike' in Southern Hemisphere

Peter Russell

June 19, 2019

The number of influenza cases in parts of the southern hemisphere has spiked early this season, according to latest indicators.

Media reports from areas of Australia in the past week have described a surge in demand for hospital beds, and  emergency departments "flooded" with people presenting with flu-like symptoms.

The Australian government's Department of Health reported high levels of flu activity for the time of year compared to previous years, with the majority of cases (81%) being influenza 'A'.

However, it said it was not possible to predict the potential severity of the season at this stage.

New Zealand's Ministry of Health said this week that some practices had run out of the flu vaccine.

Experts agree that the flu season started early, and that careful monitoring is needed to see if it has implications for our 2019-20 flu season in the northern hemisphere.

However, it remains unclear whether the experiences of Australia and New Zealand mean that flu is currently more severe than in previous years. In Hong Kong, for instance, overall seasonal influenza activity remained below the baseline level up until the week ending 8th June.

Medscape UK asked Andrew Easton, professor of virology at the University of Warwick, for his analysis of the current flu situation.

Q&A

What do we know about flu in the southern hemisphere this season?

The thing that seems striking at the moment is that the upward curve this year has started quite considerably earlier than in previous years.

What that means isn't quite so clear.

It could mean that it's started earlier and it will still peak at the same time, so it will just be a broader spread, maybe no greater numbers.

Or alternatively, it could be that the whole seasonal outbreak is going to occur and peak earlier than it has done previously; so, it could start earlier and peak earlier than it has done previously. That would be quite a major change from the pattern that we have seen because one of the reassuring things about looking at respiratory viruses in seasons is that they tend to be remarkably consistent – a little bit of drift here and there from start to finish – but pretty much they tend to be consistent.

So, at this stage we don't know the answer but that's something that we'll have to look at very carefully to see if the whole seasonal outbreak has moved forward in the calendar year. That would be extremely unusual.

Is there any indication that when flu does spike earlier in a season, it might indicate that flu will be more burdensome than usual?

It hasn't been noticed before. It doesn't really change that much.

Even a change in the pattern is not necessarily predictive of the severity of the disease that's going to arise.

So, is it the case that the reports we've seen in, for instance, parts of Australia about hospitals being inundated with patients may not mean they'll continue to be inundated but that they are just busier than normal at this point in the season?

That's right. We don't know the answer to that, and we won't know for several weeks, or months.

But we do know in Australia as a whole that flu activity has so far been higher for this time of year than in previous years.

Why might the flu season be earlier?

There can be many reasons for that. The first and obvious one is that the virus has appeared earlier.

But what will have to be looked into more closely is whether this is simply a reflection that people are being referred more frequently – you find more things the more often you look. I think that's less likely because there's a fairly standard approach to these things. But of course, if you were a clinician, and you know through your experience when to expect flu, and people start coming with flu-like illnesses early, then you may refer them more frequently to find out what's going on.

We've seen some early surveillance reports about the types of flu in circulation in Australia. Is there anything remarkable about these?

Not really, no. The focus is primarily on flu 'A' there, and they talk of two types, H3N2 and H1N1 – the standard types that are co-circulating at the moment.

In some years, the H1N1 will predominate, and in other years it's H3N2.

It's too early to predict which one is going to be linked with the more frequent, more severe, cases.

At the moment H3N2 seems to be more predominant, at least in Australia.

That's been seen before, and you can't infer too much at this stage.

The appearance of the viruses in the southern hemisphere is used to inform where necessary any re-focus of the vaccine that might be used in the northern hemisphere in our coming winter. The companies will already be tooled up to making the vaccine that we will be getting in the winter months here.

Could there be any changes?

Unlikely, for two reasons. One is that I don't think there appears to be any reason to make any dramatic changes.

But also the production is already ongoing, so it's very hard to change that once it's started.

It's a huge, huge exercise for these organisations to produce enough vaccine for a whole hemisphere.

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