FEI has announced that they have approved new regulations for the competitions that start April 12. These are temporary rules that are in force until May 30, 2021, and will be extended if necessary.
EHV-1
Competitions in which more than 400 horses are held must ensure that the horses pass a negative PCR test at least 120 hours before arrival. First FEI decided that 96 hours before arrival was required, but that has been extended.
You can find the full regulations here.