Flu shots contain influenza viruses that are grown in chicken eggs, a technology that was developed 70 years ago for making vaccines.
The problem is that flu viruses are known to make mutations inside a chicken egg to make the virus better at infecting birds. This makes it harder for a person’s immune system to recognize the virus.
These mutations can cause a person to make antibodies to the virus that are 1,000-times weaker, according to a study from researchers at The Scripps Research Institute in La Jolla, California.
For example, seasonal flu vaccines are only 33% effective at preventing H3N2 influenza. Dr. Ian Wilson demonstrated that mutations occur when the H3N2 virus is grown in eggs, which explains why the vaccines are especially bad at preventing H3N2 infections.
The mutation changes hemagglutinin, a flu protein that is a major target of antibodies in the body of a person who is vaccinated. The mutation changes how the protein binds to cells the virus infects.
The problem is that the mutation also makes it harder for the immune system to recognize actual flu viruses and prevent infections.
Dirk Zajonc, an associate professor at the La Jolla Institute of Allergy & Immunology, explained:
The immune system simply doesn’t encounter the same virus that it has seen during immunization.”
There are two flu vaccines that aren’t grown in eggs. One is Flucelvax®, a cell-based flu shot made in dog kidney cells that were taken from a Cocker Spaniel in 1958 and grown in a lab ever since.
The other cell-based flu vaccine is Flublok®, which is grown in the cells of an insect Spodoptera frugiperda, a moth known as the “fall armyworm” that mainly attacks corn crops in North America.
Source: A structural explanation for the low effectiveness of the seasonal influenza H3N2 vaccine.