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. 2015 Nov 15;61 Suppl 5(Suppl 5):S547-53.
doi: 10.1093/cid/civ602.

Population-Level Persistence of Immunity 2 Years After the PsA-TT Mass-Vaccination Campaign in Mali

Nicole E Basta  1 , Ray Borrow  2 , Abdoulaye Berthe  3 , Awa Traoré Eps Dembélé  3 , Uma Onwuchekwa  3 , Kelly Townsend  2 , Rahamatou M Boukary  2 , Lesley Mabey  2 , Helen Findlow  2 , Xilian Bai  2 , Samba O Sow  3
Affiliations

Population-Level Persistence of Immunity 2 Years After the PsA-TT Mass-Vaccination Campaign in Mali

Nicole E Basta et al. Clin Infect Dis. .

Abstract

Background: In 2010, Africa's first preventive meningococcal mass vaccination campaign was launched using a newly developed Neisseria meningitidis group A (NmA) polysaccharide-tetanus toxoid conjugate vaccine, PsA-TT (MenAfriVac), designed specifically for the meningitis belt. Given PsA-TT's recent introduction, the duration of protection against meningococcal group A is unknown.

Methods: We conducted a household-based, age-stratified seroprevalence survey in Bamako, Mali, in 2012, 2 years after the vaccination campaign targeted all 1- to 29-year-olds. Randomly selected participants who had been eligible for PsA-TT provided a blood sample and responded to a questionnaire. Sera were analyzed to assess NmA-specific serum bactericidal antibody titers using rabbit complement (rSBA) and NmA-specific immunoglobulin G (IgG) by enzyme-linked immunosorbent assay. The proportion of participants putatively protected and the age group- and sex-specific rSBA geometric mean titers (GMTs) and IgG geometric mean concentrations (GMCs) were determined.

Results: Two years postvaccination, nearly all of the 800 participants (99.0%; 95% confidence interval [CI], 98.3%-99.7%) maintained NmA-specific rSBA titers ≥8, the accepted threshold for protection; 98.6% (95% CI, 97.8%-99.4%) had titers ≥128, and 89.5% (95% CI, 87.4%-91.6%) had titers ≥1024. The rSBA GMTs were significantly higher in females than in males aged <18 years at vaccination (P < .0001). NmA-specific IgG levels ≥2 µg/mL were found in 88.5% (95% CI, 86.3%-90.7%) of participants.

Conclusions: Two years after PsA-TT introduction, a very high proportion of the population targeted for vaccination maintains high antibody titers against NmA. Assessing the duration of protection provided by PsA-TT is a priority for implementing evidence-based vaccination strategies. Representative, population-based seroprevalence studies complement clinical trials and provide this key evidence.

Keywords: Africa; immunity; meningococcal vaccines; seroprevalence.

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Figures

Figure 1.
Figure 1.
Reverse cumulative distribution of Neisseria meningitidis (NmA)–specific serum bactericidal antibody titers using rabbit complement (rSBA) by age group and sex 2 years after PsA-TT vaccine introduction in Bamako, Mali.
Figure 2.
Figure 2.
Percentage of participants with Neisseria meningitidis (NmA)–specific immunoglobulin G (IgG) concentrations ≥2 µg/mL by age group and sex 2 years after PsA-TT vaccine introduction in Bamako, Mali.
See this image and copyright information in PMC

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