How Are Seasonal Flu Vaccines Made?

Each year, a new flu shot is developed to try to combat the strains of the virus expected to wreak havoc that season. But who decides which viruses make it into the vaccine? What new technologies are being used to produce that vaccine more efficiently?

Sabrina Stierwalt, PhD
Episode #174

The virus antigens—molecular structures found on the surface of the virus’s proteins that are responsible for triggering a body’s immune response, or, in other words, the part of the virus that inspires the production of the antibodies which will eventually fight it off—are then purified. The resulting vaccine is then tested by the FDA on a lot by lot basis before approval.

According to the CDC, the process takes at least six months to produce a vaccine in large quantities. Thus, some manufacturers will make an educated guess as to which strains will need to be harvested for the upcoming flu season and will begin growing some of the virus in January, before the February meeting that produces the recommendations from the World Health Organization so that they are ready to meet demand.

In addition to the long time requirement (relative to the need for yearly updates), the egg-based manufacture of flu vaccines also requires a huge number of eggs. Certain strains of the virus grow poorly in eggs and thus our ability to inoculate against them is limited.

New Flu Shot Technology

Despite having used egg-based production methods for more than 70 years, scientists are now looking to new methods for harvesting the flu virus, in part to produce vaccines more quickly. After being grown in chicken eggs, manufacturers are allowed, since being approved by the FDA in 2012, to harvest the flu virus in canine kidney cells. This process is shorter, and obviously involves fewer eggs, but is currently only being used in one vaccine.

In 2013, the FDA approved the use of recombinant technology, a process that does not use chicken eggs at all. Manufacturers instead harvest proteins directly from the flu virus and combine them with another virus that grows well in insect cells. This combination virus is then allowed to replicate in insect cells before being harvested and purified.

The use of recombinant technology has clear advantages: it does not rely on a supply of virus-containing eggs which come from a limited number of facilities, nor is it limited to the production of vaccines against viruses that can grow well in eggs. Thus, if we face a fast-paced, Contagion-level outbreak of a flu strain, the use of recombinant DNA will allow us to respond quickly.

Who Should Get a Flu Shot?

The CDC recommends that anyone over six months of age who is not allergic to the materials used in the production of flu vaccines (like eggs!) should get a flu shot every year, especially those people who spend time around others who are particularly vulnerable to the flu like children and the elderly.

Even if, after all of the extensive data collection and research, the viruses chosen for the flu vaccine are not a good match to those that end up in circulation, the flu shot still offers some protection. Antibodies made by your body in response to the strains of flu in the vaccine can still fight against, although not as effectively, any flu virus that you contract. Every flu shot also contains protection against at least three or four strains, so even if one strain proves to not have its predicted impact, you are still inoculated against the other two or three.

Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com.

Image courtesy of Shutterstock.


About the Author

Sabrina Stierwalt, PhD

Dr. Sabrina Stierwalt is an extragalactic astrophysicist at the California Institute of Technology and Adjunct Faculty at the University of Virginia.

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