Biopharmaceutical manufacturer Bavarian Nordic announced on May 13th that significant progress was achieved in demonstrating two versions of its smallpox vaccine, Imvamune, offer satisfactory protection against infection without the adverse effects usually encountered with conventional vaccines.  The results of two separate clinical studies for the liquid-frozen and freeze-dried versions of its Imvamune vaccine moved the freeze-dried version closer to obtaining Emergency Use Authorization from the United States for its Strategic National Stockpile.

The liquid-frozen version of Imvamune was determined in a Phase 3 randomized, double-blind clinical study to cause no significant adverse reactions among 4,000 subjects (1,000 were administered a placebo) who had never been exposed to vaccinia, while providing a sufficient antibody response.  These results built on a Phase 2 study published in PLOS One in April 2015 that found the attenuated vaccinia virus (Modified Vaccinia Ankara) did not produce in 745 test subjects pericarditis or myocarditis, which are serious adverse effects often encountered with conventional smallpox vaccines.

The second clinical trial, a Phase 2 study, was used to compare the effectiveness and safety of the freeze-dried version to the liquid-frozen version of the Imvamune vaccine.  Among 650 vaccinia-naïve subjects, a roughly equivalent immunologic response without the indication of serious cardiotoxicity was found in the freeze-dried version as with the liquid-frozen version, and in congruence with results from the Phase 3 study above.  The significance of the second study is that smallpox must be lyphophilized to allow it to be stored for an indefinite, extended amount of time (usually at -20°C), as would be necessary to include it in the Strategic National Stockpile.  The next step for the Imvamune vaccine is to scale-up its freeze-drying manufacturing process.

Steven Smith, M.Sc. is an Infectious diseases epidemiologist