Dr Catherine Conlon: Are we facing a harsh flu season this year?

It’s difficult to predict how severe the flu season will be – early signals suggest it could be harsh due to a combination of lagging vaccination rates and what is being seen elsewhere in distant countries including Australia and Japan.

In Australia and New Zealand, a strain of influenza, called H3N2 surged in September and October. Meanwhile, Japan declared an influenza epidemic in early October, some five weeks ahead of the usual start of the flu season in that country.

It is too soon to say with certainty which strains will be dominant in Europe this year, but flu experts are predicting it could be the worst flu season for a decade.

Scientists track the evolution of influenza viruses because they continually mutate requiring the seasonal flu vaccine to be updated each year to keep up.

Normally, the virus drifts along making minor changes and then periodically there is a sudden abrupt shift as the virus mutates substantially.

Flu experts say such a substantial mutation happened in June this year.

Director of the centre for pathogen evolution at the UK University of Cambridge, Prof Derek Smith said in early November that seven mutations appeared in a strain of H3N2 seasonal flu and led to a “fast increase” in reports of the mutated virus.

“It almost certainly will sweep the world, so from that standpoint, it’s something that will come up quickly,” predicted Prof Smith.

The experts predict that the mutations will help the virus to evade some of the immunity we have built up over years of flu infections and vaccines.

“It’s highly likely it’s going to be a bad flu season and it’s going to happen quite soon,” said Prof Christophe Fraser, from the Pandemic Institute at the University of Oxford earlier this month.

“There are indicators that this could be worse than some of the flu seasons we’ve seen in the last 10 years.”

Up to one in five Europeans is infected with influenza every winter and it is associated with about 27,600 deaths annually across the EU, according to the ECDC.

Despite this, vaccination rates have fallen across Europe in recent years that could impact harshly on the flu season.

Getting vaccinated ahead of flu season is the best way to protect against the virus and relieve pressure on hospitals. The vaccine is updated every year because protection from the vaccine weakens over time, due to a combination of waning immunity and the influenza virus evolving.

The ECDC report that the flu vaccination coverage target for those aged 65 and over is 75% but that during the last flu season, most countries reported “well below” 50%. Ireland was one of the highest at 75% coverage with Denmark (76%), Portugal (71%) and Sweden (68%).

However, a key group that have low vaccination rates in recent years is healthcare workers. This has implications for healthcare workers themselves but also for those under their care.

This year, the HSE have put out an urgent call for all healthcare workers to receive the vaccine – not just to protect themselves but to protect their patients – many of whom may be vulnerable to a serious and potentially fatal illness.

The target for flu vaccine uptake among healthcare workers is 75%. The reality is that uptake is a fraction of that target and hit its lowest level in over a decade in the 2024/ 2025 flu season with just under a third (32%) of Irish healthcare workers receiving the flu shot. This compares to just over half (50.3%) in the 2023-24 season, according to data from the HPSC.

The decision on the design of the vaccine was made earlier in the year prior to the appearance of the new mutated virus in June. While the amount of protection offered by the vaccine may be less than in previous years when the match was better, the experts advise that the vaccine will still trigger the body to produce antibodies that will lessen the severity of disease.

“Whatever strains do circulate here this winter, we can be confident that the vaccine will still help give some protection to those most vulnerable from developing serious illness and being hospitalised,” advised Dr Mary Ramsey, director of public health programmes at the UK Health Security Agency earlier this month.

The HSE is urging anyone eligible for the flu vaccine to do so now before the season ramps up as it is likely to do over the coming weeks. This includes all those who are:

• Aged 60 and older
• Age 2 to 17
• A healthcare worker
• Pregnant
• Living in a nursing home or other long-term care facility
• In regular contact with pigs, poultry or waterfowl
• Someone with a health conditions that puts you at higher risk of flu (age 6 months or older)
• Living with living with someone who has a health condition that puts them at higher risk of flu
• A carer for someone who has a health condition that puts them at higher risk of flu

The bottom line is that it’s looking possible that we may be facing a very bad flu season this year and the best thing we can all do now to tackle the problem is to get vaccinated.

• Dr Catherine Conlon is a public health doctor in Cork – views are her own.