A 7-year-old boy presents to your office as a new patient. While reviewing his previous records, you determine that he only received one varicella vaccine when he was 4 years of age. His history is negative for primary varicella infection. Which of the following is the best next step for this patient? Administer a dose of varicella vaccine and schedule him to return in 28 days for another dose Administer a second, and final, dose of varicella vaccine Do nothing as he is considered fully vaccinated Restart the vaccine series with two doses 3 months apart