The US Food and Drug Administration (FDA) has approved expanded use of Emergent BioSolutions' EBS.N ACAM2000 smallpox vaccine to include people at high risk for mpox infection, the company said on Thursday.

Earlier this month, the World Health Organization declared mpox a global public health emergency for the second time in two years as a new variant of the virus, known as clade Ib, spread rapidly in Africa.

The FDA's approval follows Emergent's application for an Emergency Use Listing of ACAM2000 vaccine with the WHO.

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

According to the US Centers for Disease Control and Prevention, ACAM2000 has more known side effects and risks than Danish biotech Bavarian Nordic A/S's BAVA.CO Jynneos vaccine, which is approved in the United States for both smallpox and mpox.

ACAM2000 - a live, replicating virus vaccine - is known to cause myocarditis/pericarditis - swelling in or around the heart muscle - in 1 in 175 new ACAM2000 vaccine recipients, according to the FDA.