(Reuters) – Shares of some mpox vaccine and drug developers jumped sharply on Monday in premarket trading, putting them on track to extend gains from last week as concerns over an outbreak of the virus rise.

Shares of GeoVax Labs and Tonix Pharmaceuticals led the gains. Both the companies, which have a combined market capitalization of less than $50 million, do not have any products on the market.

GeoVax’s shares rose 47.9% to $10.44, while Tonix jumped 41% to 63 cents.

Emergent BioSolutions’ shares rose 5.4% to $11.32 premarket. Its vaccine, approved for smallpox, has been used as an mpox shot, but the U.S. Food and Drug Administration is yet to approve its application for use against the virus.

A new variant of mpox has spread rapidly in Africa, prompting the World Health Organization to declare mpox a global public health emergency last Wednesday.

Europe’s disease prevention agency said on Friday more imported cases will appear in the region, a day after Sweden reported its first case of mpox linked to the new strain.

Danish-listed shares of Bavarian Nordic, which makes an mpox vaccine, were down 4.1% at 271.80 Danish crowns ($40.22). They had jumped 20% on Friday, and rose 50% last week on growing concerns over the virus.

Siga Technologies’ shares were up 1.3%. The stock fell nearly 20% on Thursday after the company’s mpox drug failed to meet the main goal in a study.

($1 = 6.7584 Danish crowns)

(Reporting by Puyaan Singh in Bengaluru; Editing by Shinjini Ganguli)