If an immunocompromised child has been exposed to varicella, what immediate action should be taken?

In the case of an immunocompromised child exposed to varicella (chickenpox), the most appropriate and immediate action is to administer varicella zoster immune globulin (VZIG). This is crucial because immunocompromised individuals lack the ability to mount an adequate immune response to infections, which makes them particularly vulnerable to complications from diseases like varicella.

VZIG contains antibodies against the varicella-zoster virus and can help prevent or lessen the severity of chickenpox in those who have been recently exposed, particularly in children who may not be able to receive the live attenuated vaccine due to their compromised immune status. This prophylactic measure is essential to mitigate the risk of developing severe infection and associated complications.

Monitoring for symptoms, placing the child in isolation, or administering the varicella vaccine would not provide the immediate protection required in this context. The vaccine, being a live attenuated vaccine, is generally contraindicated for immunocompromised children, and merely observing them does not provide any protective benefit against the virus.