Final answer:
The varicella vaccine should not be given to a 2-year-old for 11 months after a blood transfusion to ensure effectiveness. This precaution is similar to the careful scheduling of other vaccines, like the conjugate vaccine for N. meningitidis and the inactivated Salk polio vaccine, to maximize immune response.
Step-by-step explanation:
The varicella vaccine, which protects against chickenpox, should not be administered to a 2-year-old boy for at least 11 months after receiving a blood transfusion of packed red cells. This waiting period is necessary because the components of the transfused blood can contain antibodies that may neutralize the live attenuated virus in the vaccine, thereby diminishing its effectiveness.
Just as the conjugate vaccine for N. meningitidis is designed to prompt the immune system to recognize polysaccharide capsules and can be given as early as two months of age, timing and type of vaccines are critical for optimal immunity. For instance, the switch to the Salk polio vaccine in the United States, which contains an inactivated virus, eliminated the risk of vaccine-associated transmission of polio, with a recommended schedule of four doses at specific intervals during childhood.