Plasma fibrinogen levels after vaccination with a native outer membrane vesicle vaccine for Neisseria meningitidis.

Several studies have shown plasma fibrinogen increases following some vaccinations, but the specific triggers and the kinetics of this response are not well understood. We conducted a phase I trial of an outer membrane vesicle vaccine for Neisseria meningitidis. Plasma fibrinogen was measured on days 0, 2 and 14 following each of 3 doses. The highest dose of vaccine was associated with the greatest increase in fibrinogen at day 2, which decreased by day 14. The first vaccination caused a greater increase than either subsequent vaccination. These transient increases in fibrinogen are comparable to what occurs with upper respiratory infections and have not been demonstrated to represent an increased risk of adverse vascular events.