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How does the JYNNEOS vaccine differ from replication-competent smallpox vaccines?
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smallpox
Edward Jenner vaccinating his child against smallpox; colored engraving.
The primary difference between the JYNNEOS vaccine and replication-competent smallpox vaccines, such as ACAM2000, lies in their ability to replicate within human cells.
- Replication-competent vaccines: Vaccines like ACAM2000 contain live, replication-competent vaccinia virus. Because the virus can replicate, these vaccines are associated with a higher risk of side effects and complications, including the potential for the virus to spread from the vaccination site to other parts of the body or to other people.1
- JYNNEOS: Also known as modified vaccinia Ankara–Bavarian Nordic (MVA-BN), JYNNEOS is a live, nonreplicating vaccinia-based vaccine. Because the virus cannot replicate in human cells, it offers a more favorable safety profile.1
Due to this distinction, JYNNEOS is generally preferred for individuals who cannot safely receive replication-competent vaccines, such as those with certain skin conditions or weakened immune systems. Both vaccines are used for the prevention of smallpox, while JYNNEOS is also indicated for the prevention of mpox.1