What is a key difference between inactivated and live vaccines?

Inactivated vaccines are composed of virus or bacteria that have been killed or inactivated, meaning they cannot replicate in the host. This characteristic is crucial because it ensures that these vaccines do not pose a risk of causing disease, even in immunocompromised individuals. The immune system can still recognize the inactivated pathogens and generate an immune response, but the inability of the vaccine to replicate means that multiple doses or booster shots may be necessary to achieve long-lasting immunity.

This contrasts with live vaccines, which contain a weakened form of the virus or bacteria that is still capable of replication. Live vaccines often stimulate a stronger and more durable immune response because they mimic a natural infection more closely than inactivated vaccines do.

While some live vaccines may require refrigeration to maintain their efficacy, this is not a definitive trait distinguishing them from inactivated vaccines, nor does it speak to their fundamental nature in terms of replication or immune response.