TribLIVE's Daily and Weekly email newsletters deliver the news you want and information you need, right to your inbox. Some coronavirus vaccine appointments at Excela Health’s North Huntingdon clinic have been going unfilled, causing concern that demand is dropping while new positive cases rise. An increase in supply allowed the health system to streamline its registry, making it easier for anyone interested in getting the vaccine to make an appointment at excelahealth.org, said Dr. Carol Fox, Excela’s chief medical officer. Officials are administering Moderna vaccines at the clinic to anyone 18 and older. “For new, first doses, I think the demand has slowed down and I don’t know if it’s vaccine hesitancy,” Fox said, or whether it is general concerns about safety after distribution of the Johnson & Johnson single-dose vaccine was paused this week because of a blood clot issue in a minuscule percentage of patients.