Flu vaccines, which are intended to help the body fight off the respiratory illness caused by the influenza virus, generally are made by injecting the virus into hen eggs. After being incubated for about three days to allow the virus to grow, the virus is removed from the egg white and processed to kill the majority of the virus and extract only the virus’s outer proteins, known as antigens. When these antigens are injected into the human body, the body's immune system develops antibodies — proteins that fight off the influenza virus. In 2013, the first flu vaccine harvested from insect cells was approved by the US Food and Drug Administration (FDA). Rather than being harvested from hen eggs, insect viruses are re-engineered to create the same influenza antigens that cause the body to develop antibodies.
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