availability. in new yor pharmacies have run out of at home tests. they are out of stock. we just came straight here. reporter: in maryland, long lines stretching around one clinic that went from testing 100 people a day to nearly a thousand. one word is discouraging. we re sad to have to be here. we are setting records not in a good way. reporter: even major retailers temporarily posting out of stock messages on their websites for popular test kits. some at home kits not arriving until after christmas. i have a nephew i m going to see so i just would like to not give them covid. reporter: the cause of the shortage? a combination of demand exceeding supply. starting with the nearly dozen companies who make the at home tests. while capacity is increasing it is not increasing as fast as our anxiety or our need. why is that? well, manufacturers are challenged with now going from one shift a day to two to three and getting enough equipment,