The World Health Organization (WHO) says it is reviewing whether any candidate Ebola vaccines or treatments could help curb an outbreak in the Democratic Republic of Congo (DRC). WHO officials describe the current surge of the highly contagious haemorrhagic fever as an international health emergency, reporting that it has killed 131 people and infected more than 500.

WHO’s DRC representative, Anne Ancia, says the organization is looking at what vaccine and treatment options are available internationally and whether any could be used in the response. WHO chief Tedros Adhanom Ghebreyesus says he is “deeply concerned” about the scale and speed of the epidemic and will convene an emergency meeting later Tuesday.

Sources also note that no vaccine or therapeutic treatment exists for the Bundibugyo strain responsible for this outbreak. Vaccines are available for the Zaire strain, but WHO technical guidance indicates that prequalified Zaire-strain vaccines cannot be used in the current response. Ancia says the WHO’s technical advisory group is set to meet to recommend which potential vaccine candidates should be prioritized, including Ervebo, though availability could take about two months.