Adapting Healthcare Defences to Fight the Flu as it Evolves

While the flu-causing influenza virus is present all year round, flu season generally picks up in October, peaks December through February, with significant activity persisting well into May. 

The flu can be very debilitating and even deadly. The Center for Disease Control (CDC) estimates that between October 2022 and April 2023, there were up to 54m people sick, up to 650,000 hospitalisations and as many as 58,000 deaths due to influenza - and that is just in the U.S., the rest of the Northern Hemisphere suffers a similar fate.

Adapting defences to fight evolving influenza strains

“Football has returned to America. Friday Night Lights, College Game Day and of course, NFL Sunday. Unfortunately, fall brings that other “F-word” and its very own season: the Flu,” shares Frederic Bertley, Chief Executive Officer at COSI, Center of Science and Industry. “On the hope front, flu vaccines are critical in the fight against influenza, but we need to develop a new flu vaccine every year.”

Much like sport, no two teams have the same offensive approach. As such, says Frederic, the defence must consistently adapt to the cleverly designed and changing offensive schemes. 

“Viruses are similar. Because of their mutation rates, they present differently, both on their genetic constitution and their antigenic presentation – that is, how they “look” to our immune system defence,” Frederic explains. “Additionally, viruses differ in their frequency of mutation, that is, how much and how fast they change over time.”

Some viruses mutate very slowly while others mutate at very high frequencies. The relevancy of this for vaccines cannot be overstated.

“Vaccines offer us protection against pathogens – in this case a virus. That protection is directly correlated with how the virus “presents itself”. If the virus wears the same clothing every time it reproduces then our immune system can recognise it with the same immune cell repertoire,” he continues. “However, if the virus is mutating at a high frequency, consistently presenting a different wardrobe, then our immune cell repertoire – our defence system – at minimum will have a hard time recognising it, or worst case, will not recognise it at all.”

The vaccine generated protection from last year, just like your favourite football team’s defensive scheme from previous seasons, will be outdated and ineffective.  This is exactly the case for influenza.  

To develop an effective flu vaccine, each year before flu season, scientists from around the world collaborate and best guess based on last year’s influenza strains, which variants will likely dominate in the upcoming months and select four of the strains to be included in next year’s seasonal vaccine campaign.  

“Sometimes the scientists get it right, but on occasion, dominant strains of the virus can change in unexpected ways, making the developed vaccine less effective,” he adds. “As of now, the estimated effectiveness of our hypothesised vaccine ranges between 49% and 60%. There are years that scientists best guess what actually happens in nature, but the reverse can also happen.”

The flu vaccine is imperfect but offers crucial protection against severe illness and potentially death

In fact, as recently as the 2014–2015 flu season, the selected strains for vaccine varied significantly from the actual circulating strains, that the vaccine efficacy was an anaemic 19% in the US, a reality that can only be retroactively calculated – at the end of the flu season.  

“By way of comparison, measles – a DNA-based virus – mutates very slowly and the typical vaccination regimen for children provides 97% protection for about the next 70 years,” he says. “If you happen to get infected with wild type measles, i.e. the disease in nature, you will literally be protected from future measles infection for life. That is the kind of immune defence system that the vaccine and wild type exposure provides. Slippery RNA-based influenza is completely different.”

You may be wondering what is the point of even taking the annual flu shot? Well, as an unapologetic scientist, Frederic likes data and the data is clear.  

“As mentioned earlier, the morbidity and mortality associated with the flu is significant. People get sick, spend time in ICU and some die,” he shares. “Furthermore, if you have preexisting conditions or certain confounders, infection with the influenza can exacerbate your illness or condition.”

Perhaps the best reason is that while you might be completely protected from being infected, the ‘dose of exposure’ – or how sick you get even if infected – can be significantly reduced because you had the vaccine with some protection, versus no protection at all.

“An analogy is to consider the flu vaccine like a bullet proof vest. The vest will not necessarily stop you from being shot at, however, if you do encounter that unfortunate fate, while the bullet impact might be uncomfortable or even hurt a little, most likely you will not be seriously hurt, let alone die,” Frederic continues. “That is why the flu vaccine is important. It will definitely protect some people from being infected in the first instance, but for those that get infected, it may very well prevent you from becoming terribly ill or even dying.”

So, just like your favourite team’s defence might not prevent every touchdown, if you prevent enough points from accumulating, certainly more than the opposition, then you come out victorious in the end. 

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