CDC data shows that as of June 16, nearly 11 percent of people who had sufficient time to get the second dose missed their ideal window. The number has increased from 8 percent earlier in the year, but CDC spokesperson Kate Fowlie said the rise was “not unexpected.” The second shot is recommended three weeks after the first Pfizer-BioNTech shot or four weeks after the first Moderna shot. Second doses were considered missed if more than 42 days had passed since the initial jab. Health officials have explained that people — in this case, nearly 15 million people — skip their second shots for a variety of reasons, such as mistakenly believing that they only need one dose to be protected. Some people also want to avoid the sometimes-unpleasant side effects that come with the second dose, and others simply miss their second appointment and can’t or don’t reschedule.