Why are live vaccines generally contraindicated during pregnancy?

Live vaccines are contraindicated during pregnancy primarily because they could potentially harm the developing fetus. Live vaccines contain a weakened form of the virus or bacteria they are designed to protect against, which has the potential to infect not only the mother but also the fetus. This poses a risk, especially during the critical periods of fetal development when the fetus is particularly vulnerable to infections and the potential for teratogenic effects.

In contrast, inactivated or killed vaccines do not carry this risk as they cannot replicate or cause disease in the body, making them safer options during pregnancy. The principle behind this contraindication is rooted in the precautionary approach to protect fetal health during a time when their organs and systems are still developing. Therefore, while maternal health is of utmost importance, the fetal risks associated with live vaccines necessitate their avoidance during pregnancy.