How Are Annual Flu Vaccines Made?

How are annual flu vaccines given?

TO Zachary Rubin edited by Kelso Harper

This video is part of “Innovations in: RSV“, an editorially independent special report produced with financial support from MSD, Sanofi And AstraZeneca.

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Zachary Rubin: Did you know that your flu shot was developed over six months ago? Yes, even before the first cough, before the onset of cold weather, scientists around the world are already working to get ahead of the virus. Here's how it works.

Twice a year, the World Health Organization convenes global experts to review influenza surveillance data. They look at which flu strains are spreading in the Southern Hemisphere winter – in places like Australia, Chile and South Africa – and use that data to predict which strains are likely to dominate the Northern Hemisphere flu season. They recommend including three to four strains in the annual flu vaccine, a decision made months before the vaccines reach your pharmacy.

Once the strains are selected, producers get to work. Most flu vaccines in the US are still egg-based, meaning the virus is actually grown inside fertilized chicken eggs. The virus is then collected, inactivated, purified and made into a vaccine.

But new methods are changing the rules of the game. Cellular vaccines grow viruses in animal cells rather than eggs. And recombinant vaccines skip the virus-growing step entirely—they use genetic engineering to quickly produce proteins that stimulate your immune system, without the need for a full-blown flu virus. These new methods are faster, can provide greater accuracy, and don't require millions of chicken eggs every year.

Even in years when the flu vaccine is less than perfect, it still prevents millions of illnesses and thousands of hospitalizations and deaths. And since the flu spreads before symptoms appear, protecting yourself helps protect your entire community.

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