Declaration of interests
KL Warfield is an employee of Emergent BioSolutions. MJ Aman is an employee of Integrated Biotherapeutics Inc. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.