Assuming your table is order by date ascending (you can force it using Table order properties), I think what you want is something like this:
if(above([Field])='Maladie' and [Field]='Jour férié' and before([Field])='Maladie' and above([DateField]=Date([DateField]-1) and before([DateField])=Date([DateField]+1),'Maladie',[Field])