Fri Mar 17

Are flu cases already 100 times higher than last year? Here's what we really know about the 2023 flu season

Written by Robert Booy, Hon Prof, Dept of Child & Adolescent Health, University of Sydney

Alarming headlines ^[1] and media coverage have said ^[2] we’ve had 100 times as many influenza cases in the first two months of 2023 compared with the same time the previous year.

The coverage suggested we’re in for a bumper flu season, starting early and your best protection was to get a flu vaccine, when available.

But that scary sounding 100 figure is misleading. Here’s what’s behind the figures and what we can really expect from the 2023 flu season.

Comparing apples with oranges

In the first two months of 2023, there were 8,474 laboratory-confirmed cases of influenza. In 2022, over the same period, there were 79 cases.

So it might seem this year’s figures are indeed more than 100 times higher than last year’s. But we shouldn’t be alarmed. That’s because in early 2022, influenza cases were artificially low.

Strict COVID measures almost eliminated ^[4] influenza outbreaks in 2020 and 2021. Shutting international borders, quarantining, social distancing and mask-wearing stopped influenza coming into the country and spreading.

Many COVID restrictions weren’t relaxed until late February/March 2022. So, in January and February of that year there were fewer opportunities for us to mingle and spread the influenza virus. It’s hardly surprising there were few cases then.

In fact, the rate of flu in 2023 is actually very similar to pre-COVID years (that is before 2020).

As always, the reported cases represent just a fraction of the actual influenza cases. That’s because many people do not seek medical care when infected with influenza or their GP doesn’t always test them for it.

How about an earlier flu season?

Every year, it seems, influenza throws a new curve ball making predictions tricky.

Flu rates in the northern hemisphere largely peaked ^[6] in December 2022, two months earlier than usual.

But there has been some late-season influenza B activity in the northern hemisphere this year. This is one type of influenza that causes seasonal flu. So travellers arriving/returning from the northern hemisphere have been bringing influenza to Australia for several months.

Travellers pulling roll-along luggage in busy airport

Travellers from the northern hemisphere may have been bringing the influenza virus with them. Shutterstock ^[7]

So we expect more cases of influenza. Australia may even have an autumn surge. This occurred last year ^[8], where influenza cases rose sharply in May, and peaked by June. That’s two months earlier than the five-year average pre-COVID.

Before COVID, influenza cases usually began to rise in April/May. This progressed to a full epidemic from June to August, often extending into September, before waning in October.

So what can we expect in 2023?

The start, length and severity of influenza seasons vary and are often unpredictable.

Community immunity will be less than in pre-COVID times. That’s because of fewer influenza infections during COVID restrictions plus lower influenza vaccine uptake ^[10] in recent years.

So the 2023 flu season may be at least moderately severe. This remains speculation. Flu routinely surprises us.

The severity of the coming Australian influenza season will be influenced by the types of influenza that circulate, when the surge starts and when the season peaks. The effectiveness, uptake and timing of vaccinations and the degree of remaining herd immunity will all be important.

Plan to get vaccinated

Only about 40% of those eligible were vaccinated against influenza in 2022, according to the Australian Immunisation Register ^[12] database. Rates were highest ^[13] in people aged 65 or older.

However, as we saw an early influenza season in 2022 (peaking in May/June) this meant many Australians were not vaccinated during the early stages of the epidemic.

With this knowledge, it’s important to be vaccinated in April/May before influenza becomes common.

Now is a good time to start preparing to get your flu vaccine. Ask your GP or pharmacist when you can book yourself in.

Vaccination is our best defence against influenza and is recommended from the age of 6 months ^[14]. Younger infants receive protection ^[15] if their mum was vaccinated during pregnancy.

The 2023 vaccine has been updated to protect against more recently circulating strains. There are also different types ^[16] of influenza vaccine, some more effective in elderly people, some free under the National Immunisation Program ^[17], some not. Other vaccines are available for people with egg allergies and for small children. It’s best to discuss the vaccine options with your GP or pharmacist.