A new approach to the definition of seroconversion following vaccination in a population with high background antibody concentrations

SEROLOGICAL RESPONSE TO CANINE DISTEMPER VACCINATION IN WILD CAUGHT RACCOONS (PROCYON LOTOR)

Canine distemper virus (CDV) is a well-known RNA virus that affects domestic dogs and all families of wild terrestrial carnivores. Spillover infections from wildlife to domestic animals are mitigated by preventive vaccination, but there is limited information on the off-label use of veterinary vaccines for wildlife like raccoons (Procyon lotor). Twenty wild-caught raccoons were inoculated with a commercial recombinant DNA canarypox-vectored CDV vaccine, applying a regimen of two serial doses by SC route with an interval of 25-28 days between doses. The CDV serum virus neutralizing antibody (VNA) baseline titers and the postvaccination titers were measured at fixed time points. Forty percent (8/20) of the wild-caught raccoons had CDV VNA titers of 1:8 or greater upon intake, and all but a single individual were juvenile animals. Approximately one month following the first vaccine dose, 8% (1/12) of raccoons seronegative at baseline had serum CDV VNA titers of 1:24 or greater. Approximately one month following the booster vaccine dose, 67% (8/12) of raccoons seronegative at baseline had serum CDV VNA titers of 1:24 or greater. Among raccoons with CDV VNA titers greater than or equal to 1:8 at baseline, 13% (1/8) demonstrated a fourfold or greater rise in titer one month after the first vaccine dose, whereas 38% (3/8) reached the same threshold one month after the booster dose. The presence of naturally acquired CDV VNA in juvenile raccoons at the time of vaccination may have interfered with the humoral VNA response. A regimen of at least two serially administered SC vaccine doses may be immunogenic for raccoons, but further investigation of alternative routes, regimens, and CDV vaccine products is also warranted for this species.

Influenza vaccination in breast cancer patients during subcutaneous trastuzumab in adjuvant setting

BACKGROUND

Despite the current recommendation for influenza vaccination in cancer patients with active oncological therapy, limited data are available on the efficacy of vaccination in cancer patients receiving targeted therapies. We aimed to investigate the immunogenicity and tolerability of influenza vaccination in breast cancer patients treated with trastuzumab in adjuvant setting.

METHODS

A prospective open-label multicenter study was performed including patients with breast cancer during trastuzumab treatment in adjuvant setting and healthy controls. Blood samples were taken before, 4 weeks after, and 12 weeks after a single dose of trivalent influenza vaccine containing inactivated A/California/7/2009 (H1N1) pdm09, A/Hongkong4801/2014 (H3N2), and B/Brisbane/60/2008. Levels of serum antibody titers to hemagglutinin for H1N1 and influenza B strains were measured.

RESULTS

Twenty breast cancer patients and 37 controls were included in the study. No difference in seroprotection rate between trastuzumab-treated patients and controls was observed for either H1N1 (100% in both groups) or B strain (78.9% vs. 89.2%, p value = 0.423). A statistically significant increase in geometric mean titers from baseline was seen in both groups and was evident both 4 weeks and 12 weeks after vaccination. Adverse events in the trastuzumab-treated group were uncommon and mild with only one serious adverse event not related to vaccination.

CONCLUSION

Breast cancer patients treated with trastuzumab in adjuvant setting seem to benefit from influenza vaccination in terms of immunogenicity without increasing the risk for adverse events. The current data support the recommendation to offer influenza vaccination in breast cancer patients treated with this type of targeted therapy.

Serostatus cutoff levels and fold increase to define seroresponse to recombinant vesicular stomatitis virus - Zaire Ebola virus envelope glycoprotein vaccine: An evidence-based analysis

The recombinant vesicular stomatitis virus - Zaire Ebola virus envelope glycoprotein (rVSVΔG-ZEBOV-GP) vaccine is a live recombinant vesicular stomatitis virus (VSV) where the VSV G protein is replaced with ZEBOV-GP. To better understand the immune response after receiving the rVSVΔG-ZEBOV-GP vaccine, the current analyses evaluated different definitions of seroresponse that differentiate vaccine and placebo recipients enrolled in a placebo-controlled clinical trial (PREVAIL; NCT02344407) in which a subset of the study participants had elevated baseline titers. Alternative values for serostatus cutoff (SSCO; 200-500 EU/mL) and/or fold rise (two- to five-fold) were applied to compare their ability to distinguish between participants receiving rVSVΔG-ZEBOV-GP or placebo. The results indicate that an SSCO of 200 EU/mL can be used to define seropositivity at baseline (i.e. pre-vaccination). The use of dual criteria of the same SSCO (200 EU/mL) together with a two-fold rise in antibody level from baseline provided the definition of seroresponse that maximized the statistical significance between vaccine recipients and placebo recipients post-vaccination. Clinical trial registration: NCT02344407.

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.