BACKGROUND: Higher density of Neisseria meningitidis carriage may be associated with transmission of the meningococcus. Our aim was to establish the impact of 4CMenB vaccine on N. meningitidis carriage density.
METHODS: We compared 4CMenB vaccine to control among 913 South Australian students aged approximately 15-18 years in a cluster randomized trial who had N. meningitidis carriage at 12 months. Oropharyngeal swabs were collected at baseline and 12 months later to detect N. meningitidis carriage. Colony forming units per millilitre (CFU/ml) were estimated by generating a standard curve that plotted qPCR cycle threshold values against log-normalized CFU.
RESULTS: Among the 913 students with N. meningitidis carriage at 12 months, there was no difference in mean carriage density between the vaccinated (n=434, 3.80 log CFU/ml [SD 1.29]) and control group (n=479, 3.73 log CFU/ml [SD 1.30]; p=0.51). Higher N. meningitidis carriage density at baseline was associated with an increase in the odds of persistent carriage at 12 months (n=504, odds ratio per 1.0 log CFU/ml increase in density = 1.36 [95% CI, 1.17, 1.58], p<0.001). Students with baseline carriage who were vaccinated had decreased persistent N. meningitidis carriage at 12 months compared to unvaccinated students (82/186 [31%] vs 105/186 [43%], odds ratio 0.60 [95% CI, 0.40, 0.90], p=0.01).
CONCLUSION: 4CMenB vaccine did not reduce carriage density of N. meningitidis 12 months post vaccination, despite increased carriage clearance. Higher carriage density is likely to enable transmission through prolonged periods of population exposure.
CLINICAL TRIALS REGISTRATION: Clinicaltrials.gov NCT03089086.
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