Every time the new school term starts, the “flu shot” climbs to the top of the parental to-do list. We know it protects our kids, but the process of creating that tiny vial is actually a marvel of global coordination and high-tech biology. If you’ve ever wondered why we need a new one every year or how they actually make the medicine, here is a peek behind the lab curtain.
The global guessing game: strain selection
The influenza virus is a master of disguise, constantly mutating its surface proteins to trick our immune systems. This is why the vaccine isn’t a one-time deal like the polio or measles shot. To stay ahead, the World Health Organization (WHO) operates a year-round global surveillance network. They monitor which flu strains are circulating in different hemispheres. Twice a year in February and September, experts meet to decide which specific strains are most likely to dominate the upcoming season.
Understanding “valency”
You might hear your doctor mention the “valency” of a vaccine, which simply refers to the number of virus strains it protects against:
- Trivalent vaccines: Historically the standard, these protect against three strains – usually two Influenza A viruses (H1N1 and H3N2) and one Influenza B virus.
- Quadrivalent vaccines: The current modern standard for most families, these protect against four strains – adding a second Influenza B virus to the mix for broader coverage.
Three ways to make the flu vaccine
Once the “recipe” for the season is set, manufacturers get to work. There are currently three primary ways to produce the flu vaccine:
Egg-based production
This is the most common and established method and has been used for over 70 years.
- The process: Scientists inject the candidate vaccine viruses into fertilised chicken eggs. The virus replicates for several days.
- The result: The fluid containing the virus is harvested. For the flu shot, the virus is inactivated (killed), and the antigen (the part that triggers your immune system) is purified.
- Note: This is why you are often asked about egg allergies, though most people with egg allergies can now safely receive the vaccine.
Cell culture-based production
Approved more recently, this method bypasses the need for millions of chicken eggs.
- The process: Instead of eggs, the flu virus is grown in cultured mammalian cells.
- The benefit: It’s a bit faster to start up than the egg method. Because the virus isn’t adapting to live in an egg environment, some studies suggest the final vaccine might be a closer match to the circulating flu viruses.
Recombinant flu vaccine
This is a high-tech approach that does not require the use of a real flu virus or eggs at any point.
- The process: Scientists isolate the gene for the hemagglutinin (HA) protein (the “spike” on the flu virus that helps it enter cells). They combine this gene with a different virus that grows well in insect cells to mass-produce the protein.
- The benefit: This process is the fastest to scale up in an emergency and is 100% egg-free.
Why the annual update?
It feels like a chore, but the annual flu shot is necessary for two main reasons:
- Viral drift: As mentioned, the flu virus changes its “look” constantly. Last year’s antibodies might not recognise this year’s version of the virus.
- Waning immunity: Our body’s immune response to the flu vaccine naturally declines over time. A yearly booster ensures your child’s defences are at peak strength when there is an outbreak.
Safety first
Regardless of the production method, every batch of flu vaccine undergoes rigorous testing for safety and potency before it reaches your doctor’s office. By getting the shot, you aren’t just protecting your child; you’re helping build herd immunity that protects grandparents and vulnerable neighbours too.
References
- https://www.cdc.gov/flu/vaccine-process/index.html
- https://www.who.int/initiatives/global-influenza-surveillance-and-response-system
- https://www.scientificamerican.com/video/how-are-annual-flu-vaccines-made/
- https://pmc.ncbi.nlm.nih.gov/articles/PMC7047267/
