On January 29, the European Medicines Agency authorized the distribution of the AstraZeneca vaccine in the European Union as one of the COVID vaccines authorized in Europe.

Why are there different vaccines? What are the differences between the vaccines developed by different laboratories and how do they work?

Unlike the Moderna and Pfizer vaccines we had until now, the AstraZeneca is of Viral Vector type, that is, it contains a genetically modified virus, while the other two are of the messenger RNA (mRNA) type.

But what does this mean?

The differences between mRNA and viral vector vaccines

The main difference is in the mechanism of action of each one.

mRNA vaccines (Moderna and Pfizer) are a new type of vaccines for protection against infectious diseases. Until now, most vaccines consisted of injecting the germ that causes the disease, attenuated or inactive, into our body, but this type of vaccine works differently.

They are formed from an artificial copy of a part of the virus's genetic code. This mRNA enters our cells to teach them to produce a protein or a portion of it and thus trigger an immune response within the body. This response produces antibodies, which are what would protect us if the virus enters us.

mRNA vaccines against COVID-19 instruct our cells to produce a harmless portion of the virus called “Spike or S protein” and is only present on the surface of the coronavirus. Once formed, our cells degrade the mRNA in about 48 hours. At no point do they cause the disease and they do not pass into the nucleus of our cells.

viral vector vaccines (AstraZeneca) contain a modified version of another virus that is less harmful than the coronavirus, which is called vectorThis vector enters our cells and uses our cellular machinery to produce the Spike protein, which as we have said before is harmless.

Once this protein is formed, due to any of the vaccines, it is displayed on its surface and our immune system recognizes it as harmful, so it triggers a response from our immune system by producing antibodies and activating other immune cells to fight what it considers to be an infection.

When the process ends, our body has learned how to defend itself and protect us in case of infection by the virus that causes COVID-19.

In both cases, the immune response is only detected with serological methods that detect antibodies to Protein S.

Comparative table of authorized covid vaccines

In addition to their mechanism of action, there are further differences that we summarize in the following table:

Source: Own elaboration Lovexair

How does a vaccine work?

When a vaccine is administered, the body generates defenses known as antibodies.

Antibodies recognize substances that are not part of the body (known as antigens), bind to them and neutralize them.

Traditional vaccines are based on administering the weakened or inactivated virus that is to be fought. The aim is for our body to generate antibodies that block it.

 What do the new vaccines have in common?

The new vaccines make our defenses act against a protein of the virus called the S protein, which is key for it to bind to the human cell.

The S protein fits into the human cell's ACE2 enzyme like a 'key in a lock,' thereby opening an entry route for the virus that causes COVID-19.

How does each vaccine work?

The European Commission has negotiated several vaccine purchase agreements (authorized Covid vaccines) with several pharmaceutical companies. The vaccines developed are of three types:

Our immune system recognizes that this protein should not be in our body and produces antibodies and T cells:

Source: Government of Spain. COVID-19 vaccination strategy

Updated: 28/12/2020

Author:

Eva Maroto López, Respiratory Physiotherapist at the Lovexair Foundation and HappyAir Coach

Bibliographic references:

Ministry of Health – Vaccination strategy (download PDF)
Spanish Agency for Medicines and Health Products (AEMPS)
Astur Health COVID-19 vaccines from viral vectors (download PDF)
Centers for Disease Control and Prevention Statement (Viral vector)
Centers for Disease Control and Prevention Statement (mRNA)

Last updated on 7 March, 2026