Prevention of meningococcal disease

The impact of pre-existing antibody on subsequent immune responses to meningococcal A-containing vaccines

Major epidemics of serogroup A meningococcal meningitis continue to affect the African meningitis belt. The development of an affordable conjugate vaccine against the disease became a priority for World Health Organization (WHO) in the late 1990s. Licensing of meningococcal vaccines has been based on serological correlates of protection alone, but such correlates might differ in different geographical regions. If high pre-vaccination antibody concentrations/titers impacts on the response to vaccination and possibly vaccine efficacy, is not clearly understood. We set out to define the pre-vaccination Meningococcal group A (Men A) antibody concentrations/titers in The Gambia and study their impact on the immunogenicity of Men A containing vaccines. Data from subjects originally enrolled in studies to test the safety and immunogenicity of the MenA vaccine recently developed for Africa meningococcal A polysaccharide conjugated to tetanus toxoid, MenAfriVac(®) (PsA-TT) were analyzed. Participants had been randomized to receive either the study vaccine PsA-TT or the reference quadrivalent plain polysaccharide vaccine containing meningococcal groups A, C, W, and Y, Mencevax(®) ACWY, GlaxoSmithKline (PsACWY) in a 2:1 ratio. Venous blood samples were collected before and 28 days after vaccination. Antibodies were assayed by enzyme-linked immunosorbent assay (ELISA) for geometric mean concentrations and serum bactericidal antibody (SBA) for functional antibody. The inter age group differences were compared using ANOVA and the pre and post-vaccination differences by t test. Over 80% of the ≥19 year olds had pre-vaccination antibody concentrations above putatively protective concentrations as compared to only 10% of 1-2 year olds. Ninety-five percent of those who received the study vaccine had ≥4-fold antibody responses if they had low pre-vaccination concentrations compared to 76% of those with high pre-vaccination concentrations. All subjects with low pre-vaccination titers attained ≥4-fold responses as compared to 76% with high titers where study vaccine was received. Our data confirm the presence of high pre-vaccination Men A antibody concentrations/titers within the African meningitis belt, with significantly higher concentrations in older individuals. Although all participants had significant increase in antibody levels following vaccination, the four-fold or greater response in antibody titers were significantly higher in individuals with lower pre-existing antibody titers, especially after receiving PsA-TT. This finding may have some implications for vaccination strategies adopted in the future.

Influenza and meningococcal vaccinations are effective in healthy subjects treated with the interleukin-1 beta-blocking antibody canakinumab: results of an open-label, parallel group, randomized, single-center study

The objective of this study was to evaluate the efficacy of influenza and meningococcal vaccines in healthy subjects exposed to the anti-interleukin-1β (anti-IL-1β) monoclonal antibody canakinumab. This was an open-label, parallel group, randomized, single-center study of healthy subjects (aged 18 to 45 years). At baseline, antibody (Ab) titers were measured and subjects were randomized (1:1) to a single 300-mg canakinumab dose administered subcutaneously (s.c.) or received no treatment (control group). After 2 weeks, subjects were treated with inactivated, unadjuvanted influenza and conjugated group C meningococcal (MenC) vaccines, administered intramuscularly (i.m.). The primary efficacy variable was the response (≥ 2-fold increase in Ab titer in ≥ 2 of 3 influenza virus strains) after 4 weeks in subjects treated with canakinumab compared to the control group. Secondary efficacy variables were the antibody response to vaccines at different thresholds and time points. Fifty-one of 112 subjects screened were randomized to canakinumab (n = 25) or the control group (n = 26). Antibody responses to vaccinations measured against different influenza virus strains and one MenC strain at 4 weeks were comparable in the canakinumab and control groups. The primary efficacy variable, the response to influenza vaccination (≥ 2-fold increase in Ab titer in ≥ 2 of 3 serotypes) at 4 weeks, was shown in 24/25 subjects in the canakinumab group compared to 25/25 subjects in the control group. Antibody responses remained comparable in the two groups at the different time points assessed. Headache was the most frequently reported adverse event. No deaths or serious adverse events were reported during the study. We concluded that a single dose of 300 mg canakinumab s.c. does not affect the induction or persistence of antibody responses after vaccination with unadjuvanted influenza or alum-adjuvanted MenC vaccines in healthy subjects.

DNA vaccines for targeting bacterial infections

DNA vaccination has been of great interest since its discovery in the 1990s due to its ability to elicit both humoral and cellular immune responses. DNA vaccines consist of a DNA plasmid containing a transgene that encodes the sequence of a target protein from a pathogen under the control of a eukaryotic promoter. This revolutionary technology has proven to be effective in animal models and four DNA vaccine products have recently been approved for veterinary use. Although few DNA vaccines against bacterial infections have been tested, the results are encouraging. Because of their versatility, safety and simplicity a wider range of organisms can be targeted by these vaccines, which shows their potential advantages to public health. This article describes the mechanism of action of DNA vaccines and their potential use for targeting bacterial infections. In addition, it provides an updated summary of the methods used to enhance immunogenicity from codon optimization and adjuvants to delivery techniques including electroporation and use of nanoparticles.