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 63% 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. Two years later, in May 2023, 100% of VASCO participants aged 18-59 and 100% 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. Another year later, in May 2023, we found N antibodies in 85% of VASCO participants aged 18-59, and 79% of those aged 60-85. This is because the Omicron variant of SARS-CoV-2 caused many infections from January on.  

In the VASCO study, participants submit blood samples at several different points in time: when they start participating and after 6, 12, 18 and 24 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. 

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 3705 BAU/ml among people aged 18-59 and 1961 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 881 BAU/ml in people aged 18-59 and 430 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 22293 BAU/ml in people aged 18-59 and 23487 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. 

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.