Insights from the COVID-19 period

In the past 3 years, COVID-19 and the coronavirus SARS-CoV-2 have been major themes in Dutch society. RIVM has been no exception. Researchers at RIVM still continue extensive research on the impact of the coronavirus on our health, our living environment, and the way we live and function. In the course of these research studies, we often work with organisations within the Netherlands and beyond, sharing knowledge and giving advice and recommendations. Read more here about the studies, partnerships and results – and about what those results mean for the future.

Laborant kijkt door microsccop

During the COVID-19 pandemic, and continuing to this day, RIVM monitors the virus and how it is spreading by means of various types of surveillance and research. Many research results are processed into models. This helps us know more about the spread of the virus and its variants

Although the Omicron variant of the coronavirus SARS-CoV-2 is less of a threat, we continue to track the virus. RIVM continues to provide a weekly update on the situation, just as we did during the pandemic. Internationally, we also continue to exchange data and information with other countries. The coronavirus SARS-CoV-2 continues to circulate in the Netherlands.

Various data sources

In the very early days of the pandemic, the spread of the coronavirus was primarily monitored based on confirmed cases reported by the Municipal Public Health Services (GGDs) and data from the Nivel monitoring stations at participating GP practices. This was supplemented by additional sources, such as data on hospital and ICU admissions provided by the NICE Foundation, and the National Coordination Centre for Patient Distribution (LCPS).

During the period that an extensive testing policy was in effect, this information was also supplemented by data from the GGD test lanes and from a partnership between doctors, laboratories and the Municipal Public Health Services (GGDs). In addition, the information derived from coronavirus monitoring in sewage research, the Infection Radar  survey and pathogen surveillance was and still is vitally important in order to continue monitoring the virus effectively. The COVID-19 vaccination campaigns were also extensively monitored, with a particular focus on vaccination coverage and vaccine effectiveness.

Coronavirus monitoring in sewage research

Detecting pathogens in sewage

Infection Radar

Vrouw doet zelftest

As more people take part, we gain more insight.

Pathogen surveillance

Collecting samples and comparing building blocks.


Watch the video: ‘Monitoring the virus’ (in Dutch, English text of audio available)

Coronavirus monitoring in sewage research

Buisjes met rioolwater voor rioolwateronderzoek

RIVM has been researching trace amounts of pathogens in Dutch sewage for years. During the outbreak of the coronavirus SARS-CoV-2 in 2020, sewage research received much more attention. Development on this type of research also accelerated dramatically. Sewage research continues to help us monitor the coronavirus. 

Important to keep track

The coronavirus SARS-CoV-2 now poses less of a threat than it did initially. This is due to the vaccinations and previous infections in the Dutch population, and because the Omicron variants are less likely to cause severe illness. Despite that, keeping track of the virus remains important. As a result, we know how often the virus occurs and where the virus is spreading, especially if it is spreading rapidly. We also know which variant is circulating, and whether a new variant is emerging. Sewage research is a very important part of this. Analysing sewage offers a very good impression of how the virus is circulating among the population. We all use the bathroom, and almost all households in the Netherlands are connected to the sewage system.

Virus particles in sewage

Human faeces from people who have COVID-19 can contain virus particles. Working with the regional water boards in the Netherlands, RIVM set up a program in which sewage samples are taken several times a week from all 300 sewage treatment plants in the country. Read more about how this research works and check out the answers to frequently asked questions on the page about coronavirus monitoring in sewage.

Also key to tracking down other diseases

Sewage research is not new. Many diseases that occur in a group of people can be detected in sewage. This could involve infectious diseases like COVID-19, but can also be used for non-infectious diseases. RIVM has been screening sewage for the poliovirus for 30 years now. Bacteria that are resistant to antibiotics are also found in sewage.

International partnerships in sewage research

RIVM has over 30 years of experience in sewage research. Within the European Union (EU European Union (European Union)), RIVM is considered an expert in this field. Other countries rely on RIVM expertise in the course of setting up and carrying out the research, and contact RIVM about data collection, analysis and modelling. The project has also been launched to expand this collaboration with other countries in the EU. Willemijn Lodder, senior researcher working in sewage research at RIVM: “This may contribute to helping us be better prepared for any subsequent pandemic. We are also exploring whether we can deploy sewage research on broader scale.” 

Vrouw doet zelftest

The first SARS-CoV-2 infection in the Netherlands was confirmed in late February of 2020. In order to monitor the spread of the virus, RIVM developed the Infection Radar survey. Every week since March 2020, Infection Radar has been compiling data on COVID-19 test results and symptoms that could indicate a SARS-CoV-2 infection.  

Infection Radar is also used to monitor the spread of other respiratory viruses, such as flu and RSV. 

Survey participants are important

Thanks to the voluntary participants in the Netherlands, Infection Radar is able to provide weekly updates throughout the year. As more people take part, we gain more insight and are able to monitor the spread of a respiratory virus more effectively. This enables RIVM to identify early warning signals and provide advice even more effectively. The health of people in the Netherlands is the main priority in this context. 

Survey questionnaire and self-test study

Over the past three years, the primary focus of the survey questionnaire was on COVID-19, with questions about the type of symptoms and the results of official tests and self-tests. This allowed us to analyse trends and patterns in the spread of the coronavirus in the Netherlands. In autumn 2022, Infection Radar was expanded to include a self-test study. Participants who used a self-test may also be asked to take a nose and throat sample. RIVM examines the sample to see whether the survey participant has COVID-19, flu or the common cold. By doing so, Infection Radar achieves a clearer overview of the respiratory viruses that cause symptoms and how these viruses are spreading.

Nice to know:

  • Since the start of the Infection Radar self-test study in October 2022, RIVM has analysed over 5,700 nose and throat samples.
  • The research results for samples from people with respiratory symptoms who tested negative for COVID-19 on a self-test showed a cold virus 1,600 times and a flu virus 250 times.
  • The most common cold viruses found in the nose and throat samples were rhinovirus and enterovirus.


Infection Radar will continue to be used and is still in development. The Infection Radar dashboard is updated every week. In addition, options are being explored for an Infection Radar app that could make it even easier for survey participants to take part. Albert Jan van Hoek, Infection Radar project lead at RIVM: “The latest news is that we will be continuing the self-test study. This enables RIVM to continue monitoring the respiratory viruses circulating in the Netherlands.” Would you also enjoy contributing to Infection Radar? Go to the Infection Radar website for more details.

Did you know that...

  • There were between 15,000 and 20,000 unique survey participants each month in winter 2022-2023. 
  • Top 5 symptoms: runny nose/nasal congestion, coughing, sore throat, sneezing and headache.
  • Something similar to the Infection Radar survey is also used in Belgium, Germany, France, Italy and England.
Zicht houden op het COVID-19 virus via computer

A virus changes constantly. The coronavirus SARS-CoV-2 is also constantly changing slightly. There are already many different variants. To monitor which variants are circulating in the Netherlands, RIVM has been examining samples containing the virus since the start of the pandemic. 

In the laboratory, all the building blocks of the genetic material from the virus (RNA) are mapped. These building blocks are compared to those of other samples. This research is known as pathogen surveillance. This shows whether the virus is changing and how. It also helps us determine if we need to be more alert regarding certain variants. We can also see how different variants of the virus are related and how they are spreading. 

Changes in the virus

This research is important to know whether the new variants that are circulating have characteristics that pose additional risks. Some changes (mutations) can cause a variant to spread more quickly or make people more ill. Other mutations change the external appearance of the virus. This makes it harder for the immune system to detect the virus after a previous infection or vaccination. 


In the early phase of the pandemic, most of the samples came from the test lanes operated by the Municipal Public Health Services (GGDs). At the peak of the pandemic, this involved up to 1,500 samples a week. RIVM also partnered with about 45 laboratories across the Netherlands. The laboratories submitted a random sampling of test samples for research purposes every week. The GGD test lanes are closed by now, so the samples that are tested by RIVM primarily come from hospitals or general practitioners. In total, more than 160,000 COVID-19 test samples were examined during the course of the pandemic. 


RIVM also maintains contact with other countries that perform pathogen surveillance. Thanks to this international network, RIVM is also aware of which variants are circulating worldwide. As a result, we can take appropriate action if, for example, a new and more contagious variant is discovered. This is how the Omicron variant was first discovered in South Africa. Because this variant was much more contagious than the variant before it, we knew that Omicron would eventually become the dominant strain in the Netherlands as well. Nearly 1,000 different variants of the coronavirus SARS-CoV-2 have been found worldwide. Dirk Eggink, virologist at RIVM: “The COVID-19 pandemic made it necessary to invest in innovative techniques and in training new employees. These investments made it possible to conduct this variant analysis research.” Read more about pathogen surveillance

(In Dutch, English closed captioning) 

In this video produced by the National Institute for Public Health and the Environment (RIVM), five RIVM employees discuss how they monitor the coronavirus.

WILLEMIJN LODDER, SENIOR RESEARCHER WORKING IN SEWAGE RESEARCH AT RIVM: “Obviously, this means that the lab was completely full of vials containing sewage samples.”

DIRK EGGINK, VIROLOGIST AT RIVM: “Our laboratory was suddenly faced with the task of analysing far greater volumes of sample material than we had previously been accustomed to seeing.”

ALBERT JAN VAN HOEK, INFECTION RADAR PROJECT LEAD AT RIVM: “At that point, there was no lockdown or other measures to prevent infections.”

FEMKE JONGENOTTER, EPIDEMIOLOGIST AT RIVM: “It had to be published at 15:00 sharp.”

TARA SMIT, EPIDEMIOLOGIST AT RIVM: “And then it was time for coffee.”

BEELDTEKST: Monitoring the virus with RIVM employees


FEMKE JONGENOTTER: “During the COVID-19 pandemic, RIVM monitored the virus very closely. New variants and new outbreaks. RIVM compiled this information and published weekly updates. Keeping track of the virus involved the efforts of many RIVM colleagues on a daily basis. We have been working as epidemiologists at RIVM since 2021. This is where we work on the weekly updates on the coronavirus that are posted every Tuesday. Basically, all the numbers come together here: sewage surveillance, pathogen surveillance, the Infection Radar survey and more. But also figures from the GGD test lanes and figures on hospital admissions.”

WILLEMIJN LODDER: “What we did from the start of the pandemic was examining sewage samples to check for the coronavirus. Since infected people excrete the virus in their stool, it ends up in sewage. This enables us to effectively monitor the virus, and helps us see which variants are circulating in the Netherlands.”

DIRK EGGINK: “Over the past 3 years, our laboratory researched the different variants of the coronavirus. There are various variants of SARS-CoV-2, each with its own specific details. That includes aspects like how contagious it is, or its susceptibility to vaccines. Because of that, it is important to know which variants are circulating in the Netherlands so the measures can be adapted appropriately in response. In recent years, we mainly analysed sample materials from the GGD test lanes to check for the different COVID-19 variants. At this point, we primarily receive samples from healthcare providers and nursing homes. We also receive sample materials from the Infection Radar study to check for the different COVID-19 variants.”

ALBERT JAN VAN HOEK: “Infection Radar is a study in which thousands of people take a survey every week to indicate whether they had relevant symptoms. Based on the increase or decrease in those symptoms and the answers to the survey questions, we can effectively monitor the spread of the coronavirus in the Netherlands. The great strength of the Infection Radar study is that we know quite a lot about our participants. Age, gender, and their risk group. This allows us to add a flood of information to sewage research, for example.”

WILLEMIJN LODDER: “We currently receive sewage samples from all of the sewage treatment plants in the Netherlands. There are more than 300 of these locations. Obviously, this means that the lab was completely full of vials containing sewage samples. We built a new lab and we were able to purchase new equipment. But we also established lots of new partnerships, for example with the regional water boards.”

DIRK EGGINK: “The COVID-19 pandemic made it necessary to invest in innovative techniques and in training new employees. These investments made it possible to conduct the variant analysis research.”

TARA SMIT: “We can hardly believe it. Two years ago, everyone was eagerly anticipating the new COVID-19 figures. The busy push to post the weekly figures started on Monday morning. We pulled all the figures together on Monday so we had the most recent overview that could be achieved, which would be published on Tuesday.”

FEMKE JONGENOTTER: “And then it was Tuesday morning. Tuesday was also incredibly busy for us. That’s when all the figures were combined to generate reports, the charts, the explanation of what it all meant, and various short videos were recorded.
Everything went online at 15:00 sharp.”

TARA SMIT: “And then it was time for coffee.”

WILLEMIJN LODDER: “Now that things are calmer, we can also start looking at what else we can use sewage research for. The Netherlands has become a pioneer in Europe in the field of sewage research by now.”

DIRK EGGINK: “In addition, the knowledge and experience we gained during the pandemic are also used for monitoring various pathogens and their different variants.”

TARA SMIT: “We are currently in an endemic phase as far as the Omicron variant is concerned. We are still monitoring the virus.”

FEMKE JONGENOTTER: “But Tuesdays are a bit less hectic.”


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