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,