Is Australia at risk of a rebound flu season?

Australia’s flu numbers have dropped dramatically since social distancing measures were implemented in mid-March, with laboratory-confirmed cases in April and May 2020 down by nearly 93% compared to the same period in the years 2010–19.
 
June is also on track to be historically low, with only 56 confirmed cases nationwide at the halfway point of the month, while the latest Australian Influenza Surveillance Report shows there have only been 36 confirmed influenza-associated deaths so far this year.
 
But while these are positive results for 2020, there are concerns it could lead to a ‘rebound’ season in 2021, particularly early in the year.
 
Professor Ian Barr, Deputy Director of the WHO Collaborating Centre for Reference and Research on Influenza at the Doherty Institute, told newsGP that while flu is ‘very unpredictable’ and the severity of seasons depends on many factors, similar rebounds have been seen previously in Australia.
 
‘Certainly, that played out in 2018–19. So, 2018 was a record low for us in the past 10 years, and in 2019 was a very big year,’ he said.
 
‘So sometimes that does happen. I don’t know whether you can lock it in, though.
 
‘What we don’t really know is how much impact there really is with having low seasons in terms of exposing people in one year or not exposing them, and then having them more susceptible the following year.
 
‘But certainly you would expect, logically, that if we have fewer people infected this year that we’ll have less herd immunity going forward, unless the vaccine can pick up some of that slack.’
 
Australia recorded 58,870 laboratory-confirmed cases in 2018 – less than 60% of the overall 2010–2019 average of 99,618 – which was followed by a record 313,360 cases in 2019, equivalent to a 432% year-on-year increase.
 
Last year’s season was also marked by an early peak. Dr Kerry Dr Kerry Hancock, Chair of the RACGP Specific Interests Respiratory Medicine network, told newsGP that can be a concern if the effect of this season’s vaccination wears off and there is no herd immunity.
 
‘We’re not quite sure what this means for next year; there hasn’t been a lot of flu in the community and therefore we don’t have that herd immunity, so we’ll be relying more on the flu vaccine,’ she said.
 
‘I think it will be a “wait and see” approach and we’ll all be a little bit anxious because we probably won’t have the vaccine for COVID-19 by early next year when the flu might potentially start to circulate again.
 
‘It will be very interesting to see next autumn and winter with regard to trying to reduce our exposure to these viruses.’
 
However, with social distancing measures beginning to relax, the latest FluTracking report shows there has already been a slight increase in people reporting influenza-like symptoms over the past two weeks.
 
Likewise, Professor Barr said children returning to schools could also see an increase in influenza cases this season.
 
‘[The last two weeks of May were] the lowest I have ever seen flu tracking,’ he said.
 
‘The question will be, what’s going to happen when schools open, can they can they really do social distancing effectively? If they can then maybe these low numbers will continue, but if they can’t –and it’s pretty hard to do – then you would expect rises.
 
‘Schools are great spreaders for [almost] everything … they’re the big spreaders, the big amplifiers of these diseases, and carrying them into homes and infecting parents and grandparents and all the rest.
 
‘Kids are a big factor, which is often overlooked.’
 
According to Professor Barr, the high number of influenza vaccinations distributed this year may also provide some protection against a bad flu season next year, and he encouraged GPs to remind patients ‘it’s not too late to be vaccinated’ as flu cases typically peak in August.
 
‘The other thing always worth considering is antivirals,’ he said.
 
‘You have your believers and your disbelievers for the influenza antivirals that are currently licensed … but I think there’s enough evidence there that for people with moderate to severe influenza that they can have an effect, especially if they’re given within 48 hours of symptoms.’
 
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