Jones & Bartlett Learning (JBL) Module 3 Practice Exam 2026 – Comprehensive All-in-One Guide to Exam Success!

Live attenuated vaccines use a weakened form of a live microorganism that can still replicate. Because this replication capability could theoretically cross the placenta and affect the developing fetus, these vaccines are typically avoided during pregnancy. In contrast, inactivated, subunit, and toxoid vaccines do not contain live organisms and cannot cause infection, so they are generally considered safe and are used when indicated (for example, certain influenza vaccines and Tdap during pregnancy). Understanding this difference explains why the live attenuated type is the one typically contraindicated in pregnancy.