Antibodies harvested from hen eggs may be used to treat COVID-19 patients or as a preventive measure for people exposed to the viral disease, according to a study.

Researchers at the University of California, Davis in the US have been able to produce antibodies to the SARS-CoV-2 spike protein in hen eggs. Spike protein is used by the virus to enter and infect the human cells.

"The beauty of the system is that you can produce a lot of antibodies in birds," said Rodrigo Gallardo, a professor at UC Davis.

"In addition to a low cost to produce these antibodies in hens, they can be updated very fast by using updated antigens to hyperimmunise hens, allowing protection against current variant strains," said Gallardo, co-author of the study published in the journal Viruses.

The researchers noted that birds produce a type of antibody called IgY, comparable to IgG in humans and other mammals. IgY does not cause allergy or set off immune reactions when injected into humans.

The antibody appears both in birds' serum and in their eggs.

"As a hen lays about 300 eggs a year, you can get a lot of IgY," Gallardo said.

The researchers immunised hens with two doses of three different vaccines based on the SARS-CoV-2 spike protein or receptor binding domain.

They measured antibodies in blood samples from the hens and in egg yolks three and six weeks after the last immunisation.

Purified antibodies were tested for their ability to block coronavirus from infecting human cells at George Mason University in Virginia, US.

Both eggs and sera from immunised hens contained antibodies that recognised SARS-CoV-2.

"Antibodies from serum were more effective in neutralising the virus, probably because there is more antibody in blood overall," Gallardo said.

Gallardo is working with colleagues at Stanford University, US, and University of Technology, Sydney, Australia to develop the egg-based antibody technology.

The team hopes to deploy these antibodies in a preventative treatment such as a spray that could be used by people at high risk of exposure to coronavirus.