Using greater than or less than today as a criteria in a countifs

You can adjust the size of the range for counting vacations based on two dates by using the Offset formula.

e.g.
=OFFSET(CalStartDate,1,CalToday-CalStartDate,10,COUNT($B$10:$ZZ$10)-(CalToday-CalStartDate))

CalstartDate is a named cell containing the first date of your vacation calendar.
CalToday is a named cell containing the current date.

Assuming your table headers (dates) are in row 10, Names are in column A and there are 10 people listed then the above offset formula would return the range of cells after today for the whole table.
Put the function in named ranges using the name manager and call it "CalcRange"

The countif formula then becomes =COUNTIF(CalcRange,"=Vac") to count all vacations after today

See example below

DynRangeEx.xlsx