#35. Sickly Stealth Attack
A Survival Kit to Staying Healthy on Global Travel
My body slumped, and I felt like I had reincarnated as a koala, requiring 18 hours of sleep each day. For the first time in my trip, I was completely depleted, and my body demanded a full recovery. Literally days into the flu season In the Northern Hemisphere (Autumn – September), I found myself succumbing to the illness.
As someone who spends a significant amount of time socialising, working in public settings, and interacting with unwell people in hospitals, I typically get vaccinated annually, without hesitation. It's well-established that vaccination reduces the severity of illness and can even prevent infection for an individual and reduce transmission within a population. However, this year my flu vaccination didn’t quite work in the way it was intended…
The Elusive Nature of the Influenza Virus
Influenza is one of the most evasive and rapidly shapeshifting viruses known to humankind and this is one of the reasons we require yearly vaccinations. The virus undergoes two primary types of genetic changes that change its ‘appearance’ over time, kind of like Mr Potato Head changing body parts.
The two genetic process changes are known as antigenic drift and shift (1). Figure 1 describes this visually.
Drift: This is a gradual process where the virus accumulates small mutations over time, leading to minor changes in its surface proteins. While these changes may not significantly alter the virus's behavior, they can reduce the effectiveness of existing vaccines.
Shift: This is a more dramatic change that occurs when two different influenza viruses infect the same cell and combine to create a new strain. This process can result in significant changes to the virus's surface proteins, making it unrecognisable to the immune system. As a result, new strains can cause widespread outbreaks and pandemics.
Figure 1 – Influenza genetic variation over time
The Science of Seasonal Prediction
The World Health Organization (WHO) plays a crucial role in coordinating the global monitoring/surveillance of influenza activity and recommending vaccine compositions to manufacturers. Twice a year, WHO convenes a meeting of experts to analyse influenza virus surveillance data and make recommendations for the upcoming flu season. This is a complex process of predictive modeling based on upcoming treats and predicted dominant strains within the population. The final output of recommendations is used by national regulatory agencies and pharmaceutical companies to develop and produce vaccines.
The most recent flu vaccine recommendations for the 2024-2025 northern hemisphere influenza season were announced in February 2024 and the southern hemisphere recommendations were announced in September 2024 (2,3). I highlighted the slight differences in Table 1. If you want to better understand the naming conventions have a read of this reference from CDC (4).
Table 1 - The WHO recommendations for trivalent vaccines for use in the 2024-2025 northern hemisphere influenza season (2,3)
Bonus note: For quadrivalent vaccines B/Phuket/3073/2013 (B/Yamagata lineage) was a consistent recommendation for both the northern and southern hemispheres.
Extra bonus note: The host of origin (eg. swine, avian, equine) is included in the naming convention, but if it’s from a human it isn’t included at all.
From The Same Mold but In Different Forms
You’ve probably noticed the lettering at the start of recommendations so it’s worth noting that there are four types of influenza viruses: A, B, C, and D. While types B, C, and D have not caused pandemics to date, type A viruses are responsible for major outbreaks. For example the 1918 pandemic and the 2009 H1N1 pandemic, otherwise known as “swine flu”, were influenza A virus outbreaks from a pig origin.
Influenza A and B viruses have the highest interest from epidemiologists. Only influenza A viruses have been responsible for pandemics to date and influenza B viruses only effect people, not animals, and typically they don’t spread to pandemic levels.
Influenza C viruses typically cause milder infections and are not associated with major outbreaks or pandemics. Influenza C primarily affects children.
Influenza D viruses primarily affects cattle is not known to infect humans so it is not often spoken about.
In summary, when people talk about the flu, they’re referencing influenza A and B viruses. They’re the influenza types that are responsible for our annual flu season, regardless of which hemisphere you’re in.
Figure 2 – Summary of the influenza virus types
The Production Pipeline for Manufacturers
To combat the ever-evolving influenza virus, scientists have developed various technologies to produce vaccines (5). The three primary methods include:
Egg-based Vaccines: This traditional method involves injecting the virus into fertilized chicken eggs. The virus replicates within the eggs, producing viral proteins that are then used to create the vaccine.
Cell Culture-Based Vaccines: This method involves growing the virus in mammalian cells, such as those from dogs or monkeys. This approach offers several advantages over egg-based production, including faster production time and the ability to produce larger quantities of vaccine.
Recombinant Vaccines: These vaccines are produced using recombinant DNA technology. By inserting specific viral genes into host cells, scientists can produce viral proteins that are then used to create the vaccine. Recombinant vaccines offer several advantages, including the ability to produce large quantities of vaccine quickly and consistently.
Irrespective of which vaccine type you chose to be vaccinated with, it takes about two weeks for the body to develop protective antibodies. While the vaccine can significantly reduce the severity of illness, its effectiveness can wane over time, typically within four to six months so it’s recommended to be administered just before the flu season starts!
The Economic Impact of Influenza
Beyond the individual health consequences, influenza imposes a significant economic burden on society. The Centers for Disease Control and Prevention (CDC) estimates that influenza accounted for 4.3–21 million medical visits, 140,000–810,000 hospitalizations, and 12,000–61,000 deaths annually in the US during the 2010–11 through 2019–20 influenza seasons (6). In turn, the estimated total economic burden of influenza is substantial at $11.2 billion (ranging from $6.3–$25.3 billion) and as high as $87.1 billion. This is a significant economic cost and only includes the US market and would be magnitudes larger for the world.
A Lesson Learned
So, what does this all mean? My personal experience highlights the importance of vaccination, especially during flu season and making sure that you receive the right vaccine, at the right time, for the right hemisphere that you’re traveling to.
By getting vaccinated, we can protect ourselves from getting sick during travels and also reducing the spread of illness through communities from the spread of illness. This advice doesn’t stop with the influenza vaccine. There are plenty of other vaccine recommendations that your pharmacist or travel medicine doctor can provide advice on depending on your travel route.
Vaccination may feel like a small step, and it can have a significant impact on public health.
Additional Photos From My Travels:
An informative read again!
I was not sure where it was leading until I got to the end. Thank you.
I'm totally fine now by the way! This was a couple of weeks ago :D