If you’ve escaped flu this year, there’s some good news: the peak of our bad flu season seems to have passed in most, if not all, parts of Australia.
But because there have been significantly more influenza cases than usual, there’s still a lot of illness around.
We asked infectious diseases experts Professor Peter Collignon from the Australian National University’s Medical School, and Professor Allen Cheng from Monash University and The Alfred Hospital to answer some common questions.
How bad has this year’s flu season been?
If you look at the result of lab tests, there’s been more than 2.5 times the number of confirmed cases of influenza compared to last year, Professor Collignon says.
But this figure is misleading because some of the rise is due to an increase in the availability of rapid testing for flu.
The number of hospital and GP visits for influenza is a much better guide and these suggest about a 50 per cent rise in flu cases, he says.
But it’s hard to say for sure until the flu season is over and all the data is collated.
Professor Cheng estimates in total, about 5 per cent of Australians will have had flu this year.
The total number of flu deaths is not yet known.
Figures collected by ABC 7.30 last week showed there had been more than 370 confirmed influenza deaths recorded in four states so far. Many of these were in aged care facilities.
Why has it been a bad flu season?
A key factor seems to be that the flu vaccine has been less effective than expected this year.
Preliminary data suggests it offered only 15 to 20 per cent protection, Professor Collignon says.
“For whatever reason, the vaccine has been very ineffective this year.”
On average, over the past 10 years, the flu vaccine protected about 40 to 50 per cent of people from infection (this is substantially less than other vaccines, like say, measles, which is about 90 per cent effective).
One reason for this is the influenza virus can mutate rapidly.
Because the vaccine has to be planned and manufactured many months ahead of the start of the flu season, the strains on which the vaccine are based may end up not being a good match with the strains of flu virus circulating.
“A lot of seasons there’s a mismatch. But even if there isn’t, the vaccine often just isn’t as effective as you’d expect it to be. We don’t know why,” Professor Collignon said.
“We really need a better vaccine. We need a different design of vaccine that … gives us protection for the next five or 10 years, no matter what strains come.”
Were the flu viruses unusually severe this year?
It seems not. It was a bad season because there were a lot more cases of flu, rather than because the viruses circulating were especially severe.
“I’m not aware of any data that shows [this year’s flu] is more virulent or aggressive,” Professor Collignon said.
The most recent Australian Influenza Surveillance Report described the clinical severity of flu this year was “low to moderate”.
Is it worth bothering with a flu shot each year?
Flu is a serious illness which can sometimes kill even apparently healthy people.
“Even though we’ve got a vaccine that’s not predictable in how well it works each year and on average might have only a 40 per cent efficacy, we’d still recommend it because that reduction is better than nothing,” Professor Collignon said.
That’s particularly important if you’re in an ‘at risk’ group for whom flu can cause very serious effects.
“If you’ve got really bad heart disease or diabetes, the last thing you need is another serious infection. It could be like the straw that breaks the camel’s back.”
Why is flu deadly?
It’s known influenza by itself can kill people because it can have overwhelming effects on your body. (This is especially the case if you have an underlying disease that already strains vital organs.)
But secondary bacterial infections are actually the most common cause of death in people with flu, Professor Collignon says.
“From all the data I’ve seen, if you die of influenza there’s around a 70 per cent chance it was a secondary bacterial infection that killed you rather than the virus by itself.”
Having flu can make a secondary bacterial infection more likely by damaging the natural mechanisms your airways use to expel bacteria when you inhale them in air.
This can make it more likely you will get infections like pneumonia, which damages your lungs so you can’t breathe properly.
What can we do to reduce secondary bacterial infections?
Taking antibiotics to reduce the risk of a secondary bacterial infection “would be a really bad idea”, Professor Collignon says.
Less than one to 2 per cent of people who get influenza will end up with a complication from it.
For everyone who gets flu to take antibiotics would lead to more bacteria being resistant to antibiotics.
That means when people really needed antibiotics, the drugs would be less likely to help them.
“We need better data to work out how we identify the small percentage who will get that secondary bacterial infection and [we also need to know] is there a rapid test we can do?
“If you’re sick with what might be influenza and, after four to five days, you start to get sicker, you should go and see a doctor and ask the specific question, ‘Could I have a bacterial secondary pneumonia?’ That is the most common life-threatening complication.”
If your doctor suspects pneumonia, he or she may organise a chest x-ray and blood test.
Has this year’s flu affected younger people versus older people differently?
There’s no evidence the proportion of younger people affected is greater this year. But absolute numbers are likely higher because of the higher number of infections overall.
It is the elderly who seem hardest hit. And it seems the vaccine was particularly ineffective in this age group.
“We’ve got essentially the same vaccine as England and Europe had last year. That vaccine appears to have been virtually completely ineffective in over 65s there. It just didn’t work at all. We don’t know why,” Professor Collignon says.
“It looks like the vaccine efficacy [in this age group] is going to be no better for us than it was in England and Europe.”
In general, older people produce a less effective immune response to vaccines than younger people.
But this year, the strain of flu that dominated in Australia (H3, a type of influenza A) is one known to cause more significant illness in the elderly. As well, it’s known this strain underwent some changes this season.
These factors may have contributed to the large number of cases in older people who had been vaccinated, Australia’s Chief Medical Officer, Professor Brendan Murphy, says.
Are we through the worst of it?
Probably yes, although in tropical regions of Australia there tends to be two flu seasons a year and the second season may not have hit there yet, Professor Cheng says.
“The ACT has less activity. It’s well and truly passed the peak,” he said.
Victoria and NSW still have, “quite a lot of flu activity” and Tasmania, Queensland and South Australia still have, “a reasonable amount of activity”.
For reasons not fully understood, Western Australia and the Northern Territory have not had as many cases of flu this year.
Professor Collignon says: “I would think in most places we are passed the peak. We still have large numbers [in some areas] though because even on the downside of the mountain, it’s still quite high compared to base [levels].”
Is it too late to get the vaccine now?
Every individual has to weigh up the potential risks and benefits of the flu vaccine for themselves. A discussion with your doctor may be helpful.
“My own personal view is you’ve missed the boat,” Professor Collignon says. “The vaccine takes at least two weeks to work.
“I would think it’s very unlikely we’re going to have large numbers of flu cases two to three weeks from now.”