Those that have anti-bodies have already been infected with the coronavirus and are temporarily at least immune from further infection. In Flanders a percentage of 4.1% of blood donors with anti-bodies was recorded on 14 April.
This is almost double the figure of 2.1% that was recorded in samples taken on 30 March. The 1,327 blood samples that were tested come from a representative cross section of the Belgian population.
The researcher that carried out the blood tests said in a press statement that "Slowly but surely herd immunity is building. However, as things stand it is still low".