In the context of the VASCO study, researchers test blood samples for antibodies against the coronavirus SARS-CoV-2. Antibodies are part of the body’s natural defences (the immune system) and indicate that a person has built up protection against the infection. Antibodies are produced after vaccination and/or infection. 

Many VASCO participants have antibodies against COVID-19

The VASCO results show a significant increase in the number of people who have antibodies against COVID-19. At the start of the study, in May 2021, 42% of people aged 18-59 and 62% of people aged 60-85 had antibodies against the coronavirus (see Figure 1, left panel). From August 2021 on, more than 90% of the VASCO participants had antibodies. This is primarily because many participants were vaccinated between May and July 2021. A year later, in May 2022, 97% of VASCO participants aged 18-59 and 95% of those aged 60-85 still had antibodies against the coronavirus. This can be attributed to booster vaccinations as well as previous infections. 

The VASCO study measures two different types of antibodies: N antibodies and S antibodies. N antibodies are only produced after a SARS-CoV-2 infection, and not after vaccination. The presence of N antibodies means that the person had a previous infection. Not everyone produces N antibodies after an infection; these antibodies are found in about 80% of people who have had a SARS-CoV-2 infection. 

In May 2021, 17% of people aged 18-59 and 10% of people aged 60-85 had N antibodies against the coronavirus (see Figure 1, right panel). That means that these people had had a SARS-CoV-2 infection. In May 2022, that percentage had risen to 61% among people aged 18-59 and 46% among people aged 60-85. This is because the Omicron variant of SARS-CoV-2 caused many infections from January 2022 on.  

In the VASCO study, participants submit blood samples at three different points in time: when they start participating, after 6 months and after 12 months. Since the participants did not all start at the same time, the samples were taken at different times for all participants. The above analysis looks at the number of participants with antibodies in their blood in relation to the number of participants who submitting a blood sample in that month. As a result, it is possible that the percentage may dip lower on occasion. 

Antibodies due to vaccination and/or infection

Skip chart Antibodies against the coronavirus SARS-CoV-2 due to vaccination and/or infection and go to datatable

Percentage of VASCO participants with antibodies against the coronavirus SARS-CoV-2 due to vaccination and/or infection (S and/or N antibodies) among people aged 18-59 and 60-85

Antibodies due to infection

Skip chart Antibodies against the coronavirus SARS-CoV-2 due to infection and go to datatable

Percentage of VASCO participants with antibodies against the coronavirus SARS-CoV-2 due to infection (N antibodies) among people aged 18-59 and 60-85.

Booster vaccination results in increased level of antibodies

Among VASCO participants, antibody levels measured shortly after the basic series of COVID-19 vaccinations were high. The median value was 3160 BAU/ml among people aged 18-59 and 1954 BAU/ml in among people aged 60-85 in the first weeks after vaccination (see Figure 2). This concerns S antibodies that are produced after vaccination. Antibody levels decreased over time. Six months after vaccination, antibody levels had dropped to a median value of 466 BAU/ml in people aged 18-59 and 428 BAU/ml in people aged 60-85. In the first month after the booster vaccination, antibody levels were higher than the levels shortly after the basic series, at a median value of 21855 BAU/ml in people aged 18-59 and 22689 BAU/ml in people aged 60-85. After the first booster vaccination, antibody levels also decreased over time. The second booster vaccination (repeat vaccination against COVID-19) among people over 60 resulted in another increase in antibody levels, back to the same high level as shortly after the first booster vaccination. 

Hoeveelheid antistoffen tegen het coronavirus door vaccinatie (S-antistoffen) na de basisserie, eerste en tweede boostervaccinatie in VASCO-deelnemers van 18-59 jaar en 60-85 jaar.

Figure 2 Levels of antibodies against the coronavirus SARS-CoV-2 due to vaccination (S antibodies) after the basic series of COVID-19 vaccinations, the first booster and the second booster in VASCO participants aged 18-59 and 60-85. The X axis shows the number of days since vaccination. Participants who had a SARS-CoV-2 infection before collecting the blood sample have not been included in this chart.
 

Upper left:
This figure shows the median level of S antibodies in BAU/ml for VASCO participants aged 18-59 years who received the basic series of COVID-19 vaccinations, by number of days since vaccination. In the first 30 days after vaccination, the median level of antibodies is high, decreasing gradually over time after vaccination. 

Upper middle:
This figure shows the median level of S antibodies in BAU/ml for VASCO participants aged 18-59 years who received the first COVID-19 booster vaccination, by number of days since vaccination. In the first 30 days after the booster vaccination, the median level of antibodies is very high, decreasing gradually over time after vaccination.

Lower left:
This figure shows the median level of S antibodies in BAU/ml for VASCO participants aged 60-85 years who received the basic series of COVID-19 vaccinations, by number of days since vaccination. In the first 30 days after vaccination, the median level of antibodies is high, decreasing gradually over time after vaccination.

Lower middle:
This figure shows the median level of S antibodies in BAU/ml for VASCO participants aged 60-85 years who received the first COVID-19 booster vaccination, by number of days since vaccination. In the first 30 days after the booster vaccination, the median level of antibodies is very high, decreasing gradually over time after vaccination.

Lower right:
This figure shows the median level of S antibodies in BAU/ml for VASCO participants aged 60-85 years who received the second COVID-19 booster vaccination, by number of days since vaccination. In the first 30 days after the second booster vaccination, the median level of antibodies is very high, decreasing gradually over time after vaccination.