Pennsylvania is facing a temporary shortage of booster shots of the Moderna vaccine after providers mistakenly used them as first doses. State health officials say the error could mean more than 100,000 people will need appointments rescheduled. The second-dose shortage does not affect the Pfizer vaccine. Pennsylvania has been holding second doses in reserve to ensure they will be available for residents who have gotten the initial shot. The state's acting health secretary Alison Beam says inconsistent vaccine supply, confusion about deliveries and a lack of clear communication caused the problem.