The FDA has expanded the approval of Emergent BioSolutions' smallpox vaccine, ACAM2000, for individuals at high risk of mpox infection, leading to a significant rise in the company's shares by over 20% pre-market. ACAM2000, which is the second approved mpox vaccine in the U.S., is not suitable for those with weakened immune systems, such as people living with HIV. This approval comes as a new strain of mpox, clade Ib, rapidly spreads in Africa, prompting the WHO to declare it a global public health emergency for the second time in two years. Emergent BioSolutions plans to donate 50,000 doses of ACAM2000 to heavily impacted African nations like the DRC, Burundi, Kenya, Rwanda, and Uganda. The vaccine has known side effects that are more pronounced than those of Bavarian Nordic's Jynneos vaccine, including risks of myocarditis. Despite previous struggles, Emergent's stock has tripled this year amid rising mpox concerns and leadership changes.