New Zealand’s winter flu season is being dominated by a type not widely seen here since before the pandemic - and known to hit our youngest hardest.

The return of long-absent influenza B comes as doctors are also seeing rising rates of respiratory syncytial virus (RSV) in hospitals - although there’s no sign yet that Covid-19 is causing the same headaches it did for our health system in last year’s “twindemic”.

At the outset of flu season, virologists flagged the potential for another bumper year of cases - particularly with influenza B making a comeback alongside the type A “swine flu” strain H1N1, and international arrival numbers returning to normal levels.

GP clinics have since seen flu rates roughly comparable with pre-pandemic years – although levels of severe acute respiratory illness (SARI) at our hospitals have been higher than even last year’s winter “twindemic” of flu and Covid-19.

ESR public health physician Dr Sarah Jefferies said there’d been a “slow and steady” rise in flu – mainly type B – since April, when flu-related hospitalisations first passed the seasonal baseline in Auckland.

“Normally, influenza is most active in July and August, but we have seen that this year’s flu season started earlier than usual,” she said.

“Both severe illness activity and community illness activity have remained low overall but have been steadily increasing in the past month.”

She suspected we were still to see the peak.

 “We are getting reports of different levels of activity in different parts of the country; Counties-Manukau, for example, is reporting higher levels than they’d usually expect to see,” she said.

Rates were also unusually high in Hawke’s Bay and Waitemata.

“Overall, I’d think there’s more to come – we’re still very early in the winter season and there’s plenty of flu circulating.”

This graph shows weekly consultation rates at a sentinel group of New Zealand GP clinics for influenza-like illnesses. 2023 is shown in blue, 2022 in dark grey, and the 2015-2019 average baseline in light grey. Image / ESR

Jefferies pointed out that influenza B tended to hit young children the worst, and that its return to New Zealand should be a good reminder that the flu vaccine was now free for children aged 6 months to 12 years.

“Influenza can affect all children mildly or seriously, even those who have never been sick,” Immunisation Advisory Centre medical advisor Dr Emma Best said.

“For those with mild asthma and those who have other medical problems, influenza is more likely to be a very serious illness,” she said.

“Influenza and other respiratory virus infections provide the pathway for serious complications such as pneumonia and life-threatening sepsis following on from the fever, runny nose and cough.”

As well, surveillance was also showing rising rates of RSV-related hospitalisations in children aged 1 to 4 years in the Auckland region.

Known to cause infections of the lungs and respiratory tract, RSV’s symptoms are usually mild and typically mimic a common cold.

But the virus can also cause severe infection in babies - especially premature infants - along with the elderly and those with weak immune systems.

In 2021, hospitals were hit hard by one of the biggest RSV waves in years – largely a result of Covid-19 restrictions having lowered levels of community immune protection.

South Auckland paediatrician and Moana Connect director associate professor Dame Teuila Percival said clinicians were now treating a lot of babies and young children with RSV, but also flu.

“There are lots of babies with bronchiolitis which is dominating our work, along with infants and children with pneumonia and flu-like illnesses,” she said.

“We are also seeing pneumonia complications such as empyema and lung abscesses.”

Meanwhile, rates of Covid-19 appeared to be tracking at relatively low levels, with the rolling seven-day average of daily new cases hovering around the 1500 mark, and weekly hospitalisations numbering in the hundreds.

That was despite the last major wave having been as long as six months ago – and genomic surveillance detecting the rise of Omicron subvariants XBB.1.16, nicknamed Arcturus, and another strain FK.1.1, thought to have evolved in New Zealand.

ESR’s health and environment science leader Dr Joanne Hewitt said wastewater sampling at 60 sites around the country indicated levels of the virus had been “relatively low and steady” since February, albeit with some regional differences.

“As of [June 9], wastewater data does not indicate an increasing number of Covid-19 infections at the national level.”