How are flu vaccines made?1,2,3
The flu changes each year, so production and development of flu vaccines varies year to year. Each year, in collaboration with the World Health Organization (WHO), the CDC predict the worst flu strains for the upcoming flu season. These recommendations are passed along to production sites to begin producing vaccines. All vaccines are tested for safety and effectiveness before distribution. In the U.S., there are currently 3 production methods for flu vaccines:
Egg-based flu vaccines
Egg-based flu vaccines are the most common method for developing flu shots or nasal flu sprays. For the flu shots, live viruses are injected into eggs, allowed to grow, harvested, then killed for use in the vaccine.
For the nasal flu sprays, weakened versions of the virus are injected into eggs, but the production methods utilized are significantly different. At the end of production, the nasal flu spray is a live, attenuated vaccine.
Cell-based Vaccines
These vaccines are similar to egg-based production methods, but utilize mammalian cells instead of chicken eggs.
Recombinant Flu Vaccines
These vaccines do not use eggs during production, instead, relying on recombinant technology. Flu markers help your immune system identify the flu quickly. Recombinant flu vaccines use these markers as the vaccine, so your immune system knows how to eliminate the virus should become infected.
Sources
1. How Influenza (Flu) Vaccines are Made. Centers for Disease Control and Prevention. https://www.cdc.gov/flu/prevent/how-fluvaccine-made.htm. Published 2019. Accessed May 4, 2020.
2. Selecting Viruses for the Seasonal Influenza Vaccines. Centers for Disease Control and Prevention. https://www.cdc.gov/flu/prevent/vaccine-selection.htm. Published 2018. Accessed May 11, 2020.
3. Influenza Vaccine Production and Design. National Institute of Allergy and Infectious Diseases. https://www.niaid.nih.gov/diseases-conditions/influenza-vaccine-product…. Published 2019. Accessed May 11, 2020.