Vitalant is urging blood donors, especially those with type O blood, to schedule appointments after its type O blood supply dropped to a two-year low. The nonprofit said the shortage worsened following the July Fourth holiday as travel reduced donor turnout. Thousands of donation appointments remain available through the end of July. Vitalant said donors who give by July 11 can receive a T-shirt while supplies last and, with a qualifying appointment, a $20 gift card. Donors who give between July 9 and Aug. 8 also will be entered to win a car valued at up to $30,000.