How COVID-19 Viral Vector Vaccines Work

This animation shows how COVID-19 viral vector vaccines, such as J&J/Janssen and AstraZeneca vaccines, deliver instructions to make the SARS-CoV-2 spike protein, so that our immune system is ready to neutralize the virus that causes COVID-19 during future encounters.


How COVID-19 viral vector vaccines work

Coronavirus. Like many viruses, coronavirus uses a protein on its surface to attach to and enter our cells.

Antibodies that fit onto this protein can block the virus from attaching. Viral vector vaccines against coronavirus teach our immune system to make these antibodies. How do viral vector vaccines do that?

Inside the virus vector is the genetic blueprint for the coronavirus surface protein. The virus vector, which is called adenovirus, is able to gain access to specialized cells of the immune system, called dendritic cells. Acting like a Trojan horse, the adenovirus enters the cell and moves toward the nucleus.

The virus vector can't cause disease, but instead delivers its specially engineered genetic material into the nucleus, where it's transcribed into messenger RNA or mRNA. That mRNA is then released back into the cell cytoplasm.

When ribosomes read this newly released mRNA, pieces of the coronavirus surface protein are made. These pieces are then displayed on the surface of the dendritic cell.

The dendritic cell travels to a nearby lymph node, where it presents the surface proteins to other cells of the immune system. Some of these cells, called helper T cells, train B cells how to make antibodies that will fit perfectly onto the surface protein of the virus.

Other cells stimulated by the protein pieces, called cytotoxic T cells, can kill virus-infected cells. Now, when the coronavirus tries to infect us, our immune system is ready. Immediately recognizing, neutralizing and destroying it, before we ever even have a chance to become sick.