It is important that vaccines work well, and offer protection against disease. 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. More information about vaccine safety is available on

Vaccine efficacy

Starting from autumn 2023, a seasonal COVID-19 vaccine once a year with an mRNA vaccine offers sufficient protection. The number of previous vaccinations is no longer checked. It is only possible for a person to receive multiple COVID-19 vaccinations within a year if prescribed by a doctor.

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 grows weaker. Vaccination helps to boost immunity.

Infection and contagiousness 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). 

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 is based on 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:

    • Updates and reports on COVID-19 vaccine effectiveness in preventing hospital and ICU admission
    • Research studies on protection by COVID-19 vaccination against infection and transmission

    The COVID-19 vaccination 

    Starting from autumn 2023, a seasonal COVID-19 vaccine once a year with an mRNA vaccine offers sufficient protection. The number of previous vaccinations is no longer checked. It is only possible for a person to receive multiple COVID-19 vaccinations within a year if prescribed by a medical specialist.

    COVID-19 vaccines in the Netherlands

    Types of COVID-19 vaccines

    • The COVID-19 vaccine made by Pfizer/BioNTech is a mRNA vaccine. This RNA vaccine 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. If 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.