These principles will be discussed later in this chapter. Several factors can interfere with replication, and these are a driving factor in the principles of timing and spacing of live vaccine.

Live vaccines must replicate in order to induce an immune response. One live vaccine licensed for use in the United States (oral adenovirus vaccine) is not attenuated. Most live vaccines used in the United States are “live attenuated”, meaning that the microbe in the vaccine is alive but has been weakened (attenuated) through serial passage in cultures, or produced through genetic technology. Vaccines can be divided into two general categories: live or non-live. Vaccines are generally recommended for members of the youngest age group at risk for experiencing the disease for which vaccine efficacy and safety have been demonstrated. Recommendations for the age at which vaccines are administered are influenced by age-specific risks for disease, age-specific risks for complications, age-specific responses to vaccination, and potential interference with the immune response by passively transferred maternal antibodies. Optimal response to a vaccine depends on multiple factors, including the type of vaccine, age of the recipient, and immune status of the recipient. General Principles for Vaccine Scheduling Major changes to the best practice guidance for timing and spacing of immunobiologics include 1) guidance for simultaneous vaccination in the context of a risk for febrile seizures and 2) clarification of the use of the grace period between doses of MMRV.

Unknown or Uncertain Vaccination Status.

Interchangeability of Single-Component Vaccines from Different Manufacturers.Spacing of Vaccines and Antibody-Containing Products.Spacing of Multiple Doses of the Same Antigen.

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