During a well-child check-up, what is the appropriate action for a nurse when a 6-month-old child has only received the first DTaP vaccine?

The appropriate action for a nurse when a 6-month-old child has only received the first DTaP vaccine is to give the second DTaP.

At 6 months, children should receive a series of three DTaP vaccinations to complete the primary immunization series. The first dose is typically given at 2 months, the second at 4 months, and the third at 6 months. Since this child has only received the first dose, administering the second dose is necessary to ensure the child is adequately protected against diphtheria, tetanus, and pertussis.

Repeating the first DTaP would not be necessary or recommended because the child has already started the vaccination series and it is important to maintain the schedule for optimal protection. Giving the measles, mumps, and rubella (MMR) vaccine is also not appropriate at this age, as it is typically administered at 12 to 15 months. Additionally, providing two DTaP vaccinations in one day is not advisable due to the risk of overwhelming the child's immune system and possible adverse reactions. Therefore, the best practice is to follow the recommended immunization schedule by administering the second DTaP vaccine.