Anthrax Vaccine Cyfendus Approved for Postexposure Prophylaxis

The Food and Drug Administration (FDA) has approved Cyfendus^™ (anthrax vaccine absorbed, adjuvanted) for postexposure prophylaxis of disease following suspected or confirmed exposure to Bacillus anthracis in persons 18 through 65 years of age when administered in conjunction with recommended antibacterial drugs.

Cyfendus is made from cell-free filtrates of microaerophilic cultures of an avirulent, nonencapsulated strain of B. anthracis. The vaccine is administered intramuscularly as a series of 2 doses (0.5mL each) two weeks apart postexposure in combination with antibacterial therapy. 

The approval was supported by data from a series of studies including a multicenter, randomized, double-blind, parallel-group phase 3 study (ClinicalTrials.gov Identifier: NCT03877926) that evaluated the lot consistency, immunogenicity, and safety of Cyfendus compared with BioThrax in adults aged 18 to 65 years.

Findings showed that 66.3% participants who received Cyfendus achieved a vaccine-induced TNA 50% neutralization factor (NF₅₀) response value ≥0.56 at day 64 (coprimary endpoint). Cyfendus was also found to be noninferior to BioThrax based on the percent difference between participants achieving a threshold TNA NF₅₀ value ≥0.29 at day 64 (coprimary endpoint).

In a phase 2 study (ClinicalTrials.gov Identifier: NCT04067011), the concomitant administration of Cyfendus with oral ciprofloxacin or doxycycline was found not to have a clinically relevant impact on the pharmacokinetics of either antibiotic or on the immunogenicity of Cyfendus. The study was conducted in males and females aged 18 to 45 years.

The most common injection-site reactions reported with Cyfendus were tenderness (88.1%), pain (86.3%), arm motion limitation (63.7%), warmth (51.2%), induration (37.5%), itching (21.9%), swelling (19.7%), and erythema/redness (17.9%). The most common systemic adverse reactions were muscle aches (75.2%), tiredness (67.1%) and headache (58.0%). 

“Cyfendus vaccine is a component of the US government’s preparedness efforts against anthrax, which remains a high-priority national security threat due to its ability to be easily disseminated, lethality, and potential for major public health impact,” said Paul Williams, Emergent’s senior vice president, products business. “The approval of the Cyfendus™ vaccine demonstrates what effective public-private partnerships can achieve for national security. Emergent will continue to work closely with the US government to transition this product to post-approval procurement while ensuring an uninterrupted supply of this important vaccine.”

Cyfendus is supplied in multiple-dose vials containing ten 0.5mL doses.