About 5 million Americans have so far missed their appointment to receive the second COVID-19 vaccine. Many Americans are reportedly choosing to miss their second dose for a variety of reasons, including a fear of potential side effects. Others had their second appointments canceled because vaccination sites ran out of doses. … The New York Times reports that nearly 8% of the people who've so far received their first dose of either the Pfizer or Moderna vaccines have missed their follow-up appointments to receive the second dose.