What is a Viral Vector Vaccine? (Infographic)

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COVID-19 vaccine vial with syringe

A third COVID-19 vaccine is available for public use after receiving Emergency Use Authorization (EUA) from the Federal Drug Administration (FDA). Dr. Stephen Rinderknecht, chair of the UnityPoint Clinic Vaccine Committee, says the Johnson & Johnson/Janssen COVID-19 vaccine is safe and effective. However, it’s a bit different than the first two COVID-19 vaccines. For instance, it’s called a viral vector vaccine.

What is a Viral Vector Vaccine?

A viral vector vaccine uses an altered and harmless virus (adenovirus) to carry genetic material to our cells. The word “vector” simply means vehicle. A viral vector vaccine is not considered a live virus vaccine, because the virus used can’t replicate.

How Does a COVID-19 Viral Vector Vaccine Work?

Here’s the step-by-step process of how a COVID-19 viral vector vaccine gets to work in the body. 


Step 1. The gene that codes for the COVID-19 spike protein is inserted into the adenovirus’ genetic material.
Step 2. This altered virus is injected into the muscle as a vaccine and heads toward our cells.
Step 3. Once inside the cell, the virus tells our cells to make the harmless COVID-19 spike protein.
Step 4. The spike protein made inside our cell moves to the cell’s surface.
Step 5. Our body notices the spike protein and an immune system response begins.

“No COVID-19 virus is used in this process, and the altered adenovirus can’t replicate. That means you can’t get COVID-19, or any other virus, from this vaccine. However, our bodies will remember the spike protein developed from the vaccine and will help protect us if we get infected by the real COVID-19 virus,” Dr. Rinderknecht says.

How Long Have Viral Vector Vaccines Been Studied?

There is currently only one licensed viral vector vaccine – for Ebola. However, that doesn’t mean it’s a new technology.

“Viruses have been studied for use as vectors since the 1970s, including work on vaccines against Zika, influenza, RSV, HIV and malaria. This process is much older technology than the mRNA vaccines, which is what’s used in the first two COVID-19 vaccines authorized for use by the FDA,” Dr. Rinderknecht says.

What’s the Difference Between Viral Vector Vaccines & mRNA Vaccines?

You’ll remember, the first two COVID-19 vaccines given Emergency Use Authorization (EUA) from the FDA are the Pfizer and Moderna vaccines. They were developed using mRNA technology. The Johnson & Johnson/Janssen vaccine is the first COVID-19 viral vector vaccine to be given Emergency Use Authorization. Despite the different processes used, these vaccines are actually very similar.

“Both the mRNA and viral vector vaccines instruct our cells to make the spike protein, which basically tricks our body’s immune system into thinking it was just infected with the COVID-19 virus. The big difference is that mRNA vaccines use a lipid particle (basically, a very tiny, fat bubble) made in the lab to deliver the genetic material. Viral vector vaccines use an altered, harmless virus to do the same thing,” Dr. Rinderknecht says.

Additionally, the virus that carries the genetic material in viral vector vaccines is much more stable, so storage temperatures aren’t so extreme. Viral vector vaccines are fast and inexpensive to make, but they aren’t as fast as the mRNA vaccines.

Why Shouldn’t the Different COVID-19 Vaccines Be Compared by Efficacy?

“Comparing how effective the different COVID-19 vaccines are is tricky, because the vaccines were tested in different geographic regions and at different times,” Dr. Rinderknecht says.

An important reminder is all three vaccines are extremely effective, especially against severe COVID-19 infection. In research, they all were 100 percent effective against hospitalization and deaths due to COVID-19.

“All three vaccines will be in limited supply for some time, and vaccine administration sites receive allocations from public health departments. Specific products are not ordered. This means the product available at any one site may not be known in advance. We strongly recommend getting whichever vaccine is available when you are eligible to get a COVID-19 vaccine,” Dr. Rinderknecht says.

What’s Next for COVID-19 Vaccines?

Dr. Rinderknecht says there are more COVID-19 vaccines on the horizon. That includes a vaccine by Novavax, which is called a protein subunit vaccine.

“Subunit protein vaccines are very common and have been used for several decades. They are made by making a protein in the lab that mimics a protein on the surface of the virus – like COVID-19 – that we are trying to prevent,” Dr. Rinderknecht says.

Examples of other subunit vaccines include the hepatitis B and pertussis vaccines.

For more information, please visit our COVID-19 vaccine page.