Chicken eggs are central to human health – and not only because they are good to eat. For the past 80 years much of the world has relied on fertile chicken eggs for the production of human flu vaccines. In the United States, for instance, an estimated 82% of the 174.5 million doses of the flu vaccine distributed in the 2019/2020 flu season were egg-based.
The basis for vaccine manufacturing is a fertilised egg that has been incubated for 10 to 11 days. It is then transferred to the vaccine manufacturer which inoculates the egg with the flu virus. In the three days that follow, the egg is put back in the hatcher and the virus incubates and replicates – just as it would in the human body. Scientists then harvest fluid containing the virus from the egg, deactivate and purify the virus, and are left with the virus antigen.
One egg delivers one vaccine dose, and the process takes at least six months.
The hatcheries and layer farms that produce vaccine eggs maintain strict biosecurity protocols, heat treat feed, UV treat water and keep the layer birds separated from the manure with slatted floors. The eggs are also disinfected multiple times during handling and transportation and are handled with extreme care to prevent cracks and losses.
Interestingly, vaccine-egg producers synchronise their operations with the human influenza season. In Brazil, for instance, the production season runs from September to April to produce eggs for the southern hemisphere’s flu season. Production stops in April, after which the houses are cleaned for a new flock in September.
Due to its unique receptors and other characteristics, the novel coronavirus cannot replicate inside eggs the way other flu viruses can. Your Covid-19 jab is, therefore, egg-free.