Experts say flu season could be worst for a decade

Flu strikes every winter, but this year seems different. Over the summer, a seasonal flu virus mutated, and it appears to be evading some of our bodies' immunity. The flu season has started more than a month early, leading the NHS to issue a 'flu jab SOS' amid fears of a brutal winter.

While there is much nuance and confusion, leading flu experts have stated that it would not be surprising if this were the worst flu season in a decade.

'We haven't seen a virus like this for a long time, so these patterns are unusual,' says Professor Nicola Lewis, head of the Francis Crick Institute's World Influenza Centre. 'It does concern me, absolutely. I'm not panicking, but I am worried.'

So, what is going on? And what can we do?

Shift and Drift

Scientists constantly monitor the evolution of influenza viruses because they change regularly, requiring the seasonal flu vaccine to be updated annually. This change occurs in a pattern described as 'shift and drift'. Most of the time, the virus makes minor changes ('drift'), but occasionally, a dramatic change ('shift') occurs.

That happened in June this year. Professor Derek Smith, director of the University of Cambridge's pathogen evolution centre, said seven mutations appeared in a strain of H3N2 seasonal flu, resulting in a 'fast rise' in reports of the mutated virus.

This happened in the middle of the northern hemisphere's summer, outside the typical flu season. 'It is almost certain that it will sweep the world,' Professor Smith says.

By September, as children returned to school, the nights drew in, and the weather began to cool, there was an increase in infections. Exactly what the mutations are doing is still being investigated, but they are clearly helping the virus to bypass some of the antibodies we have built up over years of flu viruses and vaccines. The result is that the virus is finding it easier to infect people and spread, including in countries like Japan.

If the virus can spread more easily, it does not have to wait for more favourable wintery weather—when we spend more time indoors with the heating on and windows closed—to start its season.

'I think it's going to be a severe flu season,' Professor Lewis says.

If you recall your 'R' numbers from the pandemic (the number of people each infected person passes the virus on to), the new mutant has a 'leg up'. The R number for seasonal flu is usually around 1.2, while the early estimate for this year is 1.4, said Professor Lewis. So, if 100 people had flu, they would infect 120 others in a normal year, but 140 this year.

Worst flu season for a decade?

'It's very likely it's going to be a bad flu season, and it'll take off quickly because it's just getting started,' says Professor Christophe Fraser of the University of Oxford's Pandemic Sciences Institute. 'There are signals that this flu season is going to be worse than any of the flu seasons we've seen in the last ten years.'

In a typical flu season, one in five of us gets sick; this year, it could be more. However, all these estimates are clouded by uncertainty. While Australia had one of its worst flu seasons on record this year, which some are looking at for clues, it did not face the same mutated H3N2 strain we are seeing.

We know the virus is spreading quickly in children—in the 'germ-fest' of the school playground. However, the immunity a 10-year-old has developed is very different from that of their grandparents, whose immune defences may have been shaped by six times as many flu seasons. Experts will be monitoring closely as the virus begins to infect older age groups in the coming weeks.

'It's a nastier virus'

Historically, the type of influenza we are seeing this year (H3N2) is more severe, especially for elderly people. There are several strains of flu. You may have heard of H1N1 ('swine flu'), which caused a pandemic in 2009, or H5N1 (the 'bird flu' currently affecting birds). The latest mutations have occurred within the H3N2 group.

'H3 is always a 'hotter' virus, it's a nastier virus, so it'll be more noticeable in the population,' Professor Lewis said.

It is important to note that while some people will get flu and develop no symptoms, and others will get a sudden fever, body aches, and exhaustion, it can be deadly for older and more vulnerable groups. Almost 8,000 people died from flu last year, and nearly 16,000 died in the 2022-23 flu season. The NHS is also bracing for a tough flu season.

So, what can we do about it?

The Vaccine

The simplest recommendation is to get the seasonal flu vaccine. The NHS in England issued a 'flu jab SOS', saying there were 2.4 million vaccine slots available in the upcoming week.

According to Professor Lewis, this year is 'definitely the most important year' to get vaccinated. 'If you have been called by your GP, please get your flu vaccine as soon as possible,' she urged.

However, this year's vaccine is not a perfect match for the mutated virus. The vaccine composition was chosen in February to ensure millions of doses could be manufactured, but the new mutant only appeared in June.

'Some protection is better than none,' Professor Fraser said, adding that while the match is not ideal, the vaccine will still cause the body to produce antibodies that can recognise and attack the flu. The most significant health benefits are expected to be in lessening the severity of the disease rather than stopping infection entirely.

Furthermore, the flu vaccine protects against multiple strains of flu, any of which could cause their own waves of infection. Whatever strains are circulating this winter, we can be sure the vaccine will still provide some protection to those most vulnerable to severe illness and hospitalisation.

Meanwhile, doctors have been sent an alert that early antiviral therapy can reduce the risk of flu complications. Japan, which is also experiencing an early flu season, has been closing schools to help prevent outbreaks. These are not COVID-style lockdowns, but short-term measures to stop the virus from spreading.

Nobody knows for certain what will happen in the coming months. 'It could all go away by next week,