A Phase I clinical safety trial in healthy human adults has established that BPZE1 is safe and able to transiently colonize the nasopharynx. Colonization was dose-dependent with 5 of 12 individuals being colonized in the high-dose group versus 1 of 12 in the low and medium-dose groups. Significant increases in Bordetella pertussis specific immune responses were seen in all colonized individuals, but not in any non-colonized subject. No vaccine-related serious adverse events were noted, and other adverse events were trivial and occurred with similar frequency to the placebo group (A phase I clinical study of a live attenuated Bordetella pertussis vaccine--BPZE1; a single centre, double-blind, placebo-controlled, dose-escalating study of BPZE1 given intranasally to healthy adult male volunteers. Thorstensson et al., 2014). BPZE1 is the first live attenuated bacterial vaccine specifically designed for the respiratory tract ever tested in humans.

The genetic stability and excellent pre-clinical safety profile of BPZE1 has allowed this strain to be downgraded from safety level 2 to safety level 1 in several European countries, which was a prerequisite for advancing to the phase I study. The Phase I study was performed in Sweden by the Karolinska Trial Alliance with 48 young male volunteers that had never been vaccinated against pertussis and had not knowingly experienced pertussis disease. This placebo-controlled, double-blind, dose-escalating safety trial was initiated at the end of 2010 (Clinicaltrials.gov ID: NCT01188512). Three BPZE1 doses were tested: 10^3, 10^5 and 10^7 colony-forming units delivered in a 100 µl/nostril volume to 12 subjects per dose group, and 12 subjects received 100 µl/nostril of diluent only. Subjects were followed up for 6 months after vaccination.