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Vaccination or previous infection with the coronavirus SARS-CoV-2 provide less effective protection against the Omicron variant compared to the Delta variant. A COVID-19 booster vaccination ensures renewed protection against Omicron. These findings are from research by RIVM, based on data from the test lanes of the Municipal Public Health Services (GGDs). A preprint of the research findings is available on MedRxiv.

The risk of COVID-19 from the Delta variant was 76% lower after a completed basic series of COVID-19 vaccinations and 78% lower after an infection, compared to a person who was unvaccinated and had not previously had a SARS-CoV-2 infection. Protection against infection with the Omicron variant was 33% after vaccination and 25% after a previous infection. After booster vaccination, protection against infection with Delta rose to 93%, compared to 68% protection against infection with Omicron. People who were vaccinated and had also had a previous SARS-CoV-2 infection had more effective protection against the Delta and Omicron variants than people who had only been vaccinated, or had only had a previous infection. 

Research results from the GGD test lanes

This study was conducted based on over half a million test samples from the GGD test lanes. The tests were carried out by two large laboratories between 22 November 2021 and 19 January 2022. These two laboratories performed a specific PCR test that shows whether the person had the Delta variant or the Omicron variant. The percentage of positive tests involving the Omicron variant was 0% on 22 November 2021, rising to 95% on 19 January 2022.

This study only looked at the BA.1 subvariant of the Omicron variant. Since mid-January 2022, the percentage of cases involving the BA.2 subvariant of Omicron has also been increasing in the Netherlands. At this time, it is not clear whether protection against infection with the BA.1 subvariant, resulting from vaccination and previous infection, is similarly effective in preventing infection with the BA.2 subvariant.

International research shows that protection from vaccination is more effective in preventing hospital admission (severe infection) than mild infection. Booster vaccination intensifies that protection, including protection against the Omicron variant. This means that if you do get a SARS-CoV-2 infection even after basic vaccination and booster vaccination, you have a much lower risk of becoming seriously ill.

If you have symptoms, stay home and get tested  

To prevent the virus from spreading, it is important for people to stay home if they have symptoms, and get tested by the GGD or use a self-test. This applies even if you are vaccinated or have previously had COVID-19.