To register, users provide the CDC with some basic information: where and when they got their shot, their name, and their phone number. The agency says on its website that your personal information in v-safe is protected so that it stays confidential and private.The check-ins are daily for the first week after vaccination. After that, v-safe check-ins become weekly, for up to five more weeks. Fever is a relatively common side effect of all three vaccines, affecting around 10% of people who get one shot of Pfizer, Moderna, or Johnson & Johnson's vaccine.It can be more common after the second shot of Pfizer or Moderna, affecting about one in every three patients. Arm pain is by far the most common vaccine side effect people report, with all three vaccines. Some people who've gotten Moderna's shot have also complained about swelling and itchy rashes. The arm rash will usually subside after several days. If you're concerned about a rare but serious adverse reaction to a vaccine, you can also report the issue directly to the federal Vaccine Adverse Event Reporting System (VAERS).