The FDA granted expanded approval to Emergent BioSolutions' smallpox vaccine for use by people at high risk of mpox infection.

The FDA clearance makes the vaccine, called ACAM2000, the second approved shot against mpox in the U.S. after Bavarian Nordic's Jynneos.

The Emergent vaccine, however, cannot be taken by those with weakened immune systems, including people with HIV. Its use was limited earlier during a 2022 outbreak of mpox in the U.S., even though it was part of the country's stockpile.

Both Jynneos and ACAM2000 contain vaccinia virus that is closely related to, but less harmful than, the viruses that cause smallpox and mpox. ACAM2000 uses a live, infectious form of the vaccinia virus.

Still, the approval comes at a time when a new mpox strain known as clade Ib has spread rapidly in Africa. The WHO earlier this month declared mpox a global public health emergency for the second time in two years.

"Mpox has progressed to become an uncontrolled epidemic in Africa ... creating an enormous need to use all effective tools to extinguish it as a threat," said Amesh Adalja, MD, an infectious diseases expert at Johns Hopkins Center for Health Security.

Emergent BioSolutions said it would donate 50,000 doses of its smallpox vaccine to the Democratic Republic of the Congo and other impacted countries such as Burundi, Kenya, Rwanda and Uganda to address the mpox outbreak.