My covid-19 antibody level is 50. Do I still need a second vaccination?

Question from Debbie: I am in the risk group for corona and have had 1 vaccination. Now I have been tested for antibodies for Covid-19 and my value is 50. What does this value say? Am I sufficiently protected? Should I still get my second vaccination?

A: At this time, you tested positive with sufficient antibodies above the reference value.
However, it remains to be seen how long this persists with only 1 vaccination instead of 2.

There have been some scientific studies on this, but they are about age groups, not about you personally.

https://www.nature.com/articles/s41564-021-00947-3/figures/2

All you can do is measure again after a while to see if the drop has started.

https://www.bloodtesting.nl/bloedonderzoek/covid-19-coronatesten/heb-ik-voldoende-antistoffen-na-vaccinatie/

The protection after a first vaccine is quite low, about 60%. After a 2nd vaccination you are more than 95% protected. Especially if you are in risk group, it is strongly advised to take the vaccine. The value of 50 does not say much. It increases over time, and then decreases again, but not in everyone. There is no international consensus yet on how high the titer should be for optimal protection.

https://www.bloodtesting.nl/bloedonderzoek/covid-19-coronatesten/heb-ik-covid-19-gehad/