What action should be taken for a child who received the MMR vaccine 3 weeks ago and the varicella vaccine today?

The child in this scenario is being managed appropriately, as the MMR (measles, mumps, rubella) vaccine and the varicella (chickenpox) vaccine can be administered concurrently or at different intervals, as in this case. The administration of these two vaccines does not negate the child’s ability to develop immunity against the diseases they protect against.

The MMR vaccine stimulates the immune system to protect against measles, mumps, and rubella, while the varicella vaccine induces immunity against chickenpox. When these vaccines are given, they both effectively engage the immune response, allowing the child to develop immunity to both sets of diseases.

There is no necessity to repeat the MMR vaccine or the Varicella vaccine within four weeks as long as they have been administered according to the recommended schedule. This understanding is based on the fact that the varicella vaccine can be given at the same time as or at any interval between doses of the MMR vaccine, according to CDC guidelines. Thus, the child is indeed protected against both diseases following the administration of the vaccines as specified.