It is important that vaccines work well, and offer protection against disease. At the same time, vaccines also need to be safe for your health. This page describes how COVID-19 vaccines work and how vaccine safety is assessed.

Vaccine safety

A vaccine cannot be used until it has been approved. The safety of the COVID-19 vaccines is assessed by the European Medicines Agency (EMA), and in the Netherlands also by the Medicines Evaluation Board (CBG-MEB). Even after vaccines are approved, they are monitored to assess how they work and track side effects. More information about vaccine safety is available on

Vaccine efficacy

One seasonal COVID-19 vaccination with an mRNA vaccine every autumn offers sufficient protection. It is only possible for a person to receive multiple COVID-19 vaccinations within a year if prescribed by the treating physician.

Building or refreshing resistance to the virus

Vaccination helps the body build resistance (immunity) to the virus. An infection with the coronavirus SARS-CoV-2 also helps build resistance. After that, people are less likely to become ill, or will not become seriously ill. If some time has passed since the last vaccination or infection, that protection against COVID-19 grows weaker. A follow-up vaccination helps to boost immunity again.

Risk of getting COVID-19 after vaccination

After vaccination, you may still get the virus. However, there is a much lower risk of becoming ill or developing severe symptoms, because vaccination does protect against that.

Vaccination also reduces transmission of the virus from one person to another (as shown for the Alpha, Delta and Omicron variants in the VASCO study). 

Contagiousness during COVID-19

You are contagious 1 to 2 days before you develop symptoms. The risk of infecting others is highest during the first few days after your symptoms start. This subsides quickly, and you are usually no longer contagious after 5 days.

If you are coughing and sneezing, you are more likely to transmit the virus. Be careful during contact with people in vulnerable health, who could become seriously ill from a respiratory infection. Wear a face mask that covers the mouth and nose as needed, if you have symptoms and cannot maintain physical distance from others. For more recommendations, visit the COVID-19 pages on the RIVM website.


Vaccine protection against variants of the coronavirus SARS-CoV-2

It is normal for a virus to change. Different variants of the coronavirus SARS-CoV-2 have been found all over the world. This does not mean the vaccine is no longer effective. These changes involve minimal differences in the virus. Even if a vaccine is slightly less effective against a variant, it can still offer protection against serious illness and death.

International research on vaccine efficacy

Variants of the virus are subjected to research at the national and international levels to determine how they respond to the vaccines. RIVM is also conducting research on variants of the coronavirus SARS-CoV-2. Read more on the RIVM page on Variants of the coronavirus SARS-CoV-2.

Vaccines are then adapted in response to research findings. The mRNA vaccines have been updated multiple times. The current vaccine has been adapted to the SARS-CoV-2 variant Omicron XBB.1.5.

Effectiveness of the COVID-19 vaccines

RIVM monitors whether the vaccine actually prevents severe illness and hospital admission due to COVID-19. This is known as vaccine effectiveness. RIVM investigates this by analysing data from different registries and by conducting specific research:

COVID-19 vaccines in the Netherlands 

Types of COVID-19 vaccines

  • The COVID-19 vaccine made by Pfizer/BioNTech is an mRNA vaccine. It contains a protective envelope of lipids (fat) with an instruction (code) that tells your cells to make spike proteins. These are the spiky protrusions on the exterior of the coronavirus. The immune system recognises the spike proteins as foreign substances and starts making antibodies. 
  • The Novavax vaccine is a protein subunit vaccine. The vaccine contains very small particles of spike protein, which have been produced in a laboratory. It also contains an adjuvant: a substance that intensifies the body’s immune response to the protein. After vaccination, the body responds by producing antibodies against the spike protein. When the body encounters the SARS-COV-2 virus, the immune system recognises the spike proteins on the virus. In response, the immune system starts producing antibodies.

Package leaflets for the COVID-19 vaccines

Pfizer/BioNTech (Comirnaty)  Official Dutch package leaflet Vaccine factsheet
Novavax (Nuvaxovid) Official Dutch package leaflet Vaccine factsheet

There is no gelatine, chicken protein or antibiotics in the mRNA vaccines made by Pfizer/BioNTech.

Animation: Novavax vaccine

Animation Novavax vaccine

It is now possible to vaccinate with Novavax,
a vaccine that works differently than previous mRNA and vector vaccines.

Here is how it works:
To produce antibodies and other defences against the coronavirus,
the human body has to recognise the spike proteins from the virus.

With the mRNA and vector vaccines, the body uses a blueprint to
make these spike proteins itself... and then develops defences.

Novavax is a protein subunit vaccine, so it already contains
smaller parts of the spike proteins.
When these protein subunits enter the body, it starts to produce
antibodies and other defences.

An adjuvant in the vaccine helps to create a stronger immune response.
A similar adjuvant is also in vaccines against other diseases.

Once the body has developed its immune response to the
coronavirus, it breaks down the vaccine again.

The Novavax vaccine is just as effective as other vaccines... and offers
an alternative for people who do not want an mRNA or vector vaccine
or who are allergic to them.

Like previous vaccines, Novavax was developed based on the first
COVID-19 variants... so its effectiveness against Omicron is
still being investigated.

Vaccination with Novavax consists of a basic series of 2 injections...
and a possible booster jab for this vaccine is still being researched.