Low-level viraemia among people living with HIV in Nigeria: a retrospective longitudinal cohort study.

BACKGROUND: HIV transmission can occur with a viral load of at least 200 copies per mL of blood and low-level viraemia can lead to virological failure; the threshold level at which risk for virological failure is conferred is uncertain. To better understand low-level viraemia prevalence and outcomes, we analysed retrospective longitudinal data from a large cohort of people living with HIV on antiretroviral therapy (ART) in Nigeria. METHODS: In this retrospective cohort study using previously collected longitudinal patient data, we estimated rates of virological suppression (≤50 copies per mL), low-level viraemia (51-999 copies per mL), virological non-suppression (≥1000 copies per mL), and virological failure (≥2 consecutive virological non-suppression results) among people living with HIV aged 18 years and older who initiated and received at least 24 weeks of ART at 1005 facilities in 18 Nigerian states. We analysed risk for low-level viraemia, virological non-suppression, and virological failure using log-binomial regression and mixed-effects logistic regression. FINDINGS: At first viral load for 402 668 patients during 2016-21, low-level viraemia was present in 64 480 (16·0%) individuals and virological non-suppression occurred in 46 051 (11·4%) individuals. Patients with low-level viraemia had increased risk of virological failure (adjusted relative risk 2·20, 95% CI 1·98-2·43; p<0·0001). Compared with patients with virological suppression, patients with low-level viraemia, even at 51-199 copies per mL, had increased odds of low-level viraemia and virological non-suppression at next viral load; patients on optimised ART (ie, integrase strand transfer inhibitors) had lower odds than those on non-integrase strand transfer inhibitors for the same low-level viraemia range (eg, viral load ≥1000 copies per mL following viral load 400-999 copies per mL, integrase strand transfer inhibitor: odds ratio 1·96, 95% CI 1·79-2·13; p<0·0001; non-integrase strand transfer inhibitor: 3·21, 2·90-3·55; p<0·0001). INTERPRETATION: Patients with low-level viraemia had increased risk of virological non-suppression and failure. Programmes should revise monitoring benchmarks and targets from less than 1000 copies per mL to less than 50 copies per mL to strengthen clinical outcomes and track progress to epidemic control. FUNDING: None.

Functional Activity of Antibodies Directed towards Flagellin Proteins of Non-Typhoidal Salmonella.

Non-typhoidal Salmonella (NTS) serovars Typhimurium and Enteritidis are major causes of invasive bacterial infections in children under 5 years old in sub-Saharan Africa, with case fatality rates of ~20%. There are no licensed NTS vaccines for humans. Vaccines that induce antibodies against a Salmonella Typhi surface antigen, Vi polysaccharide, significantly protect humans against typhoid fever, establishing that immune responses to Salmonella surface antigens can be protective. Flagella proteins, abundant surface antigens in Salmonella serovars that cause human disease, are also powerful immunogens, but the functional capacity of elicited anti-flagellar antibodies and their role in facilitating bacterial clearance has been unclear. We examined the ability of anti-flagellar antibodies to mediate microbial killing by immune system components in-vitro and assessed their role in protecting mice against invasive Salmonella infection. Polyclonal (hyperimmune sera) and monoclonal antibodies raised against phase 1 flagellin proteins of S. Enteritidis and S. Typhimurium facilitated bacterial uptake and killing of the homologous serovar pathogen by phagocytes. Polyclonal anti-flagellar antibodies accompanied by complement also achieved direct bacterial killing. Serum bactericidal activity was restricted to Salmonella serovars expressing the same flagellin used as immunogen. Notably, individual anti-flagellin monoclonal antibodies with complement were not bactericidal, but this biological activity was restored when different monoclonal anti-flagellin antibodies were combined. Passive transfer immunization with a monoclonal IgG antibody specific for phase 1 flagellin from S. Typhimurium protected mice against lethal challenge with a representative African invasive S. Typhimurium strain. These findings have relevance for the use of flagellin proteins in NTS vaccines, and confirm the role of anti-flagellin antibodies as mediators of protective immunity.

Sustained protection in mice immunized with fractional doses of Salmonella Enteritidis core and O polysaccharide-flagellin glycoconjugates.

Non-typhoidal Salmonella (NTS) serovars S. Enteritidis and S. Typhimurium are a major cause of invasive bacterial disease (e.g., bacteremia, meningitis) in infants and young children in sub-Saharan Africa and also occasionally cause invasive disease in highly susceptible hosts (young infants, the elderly, and immunocompromised subjects) in industrialized countries. No licensed vaccines exist against human NTS infections. NTS core and O polysaccharide (COPS) and FliC (Phase 1 flagellin subunits) each constitute protective antigens in murine models. S. Enteritidis COPS conjugated to FliC represents a promising vaccine approach that elicits binding and opsonophagocytic antibodies and protects mice against lethal challenge with virulent S. Enteritidis. We examined the protective efficacy of fractional dosages of S. Enteritidis COPS:FliC conjugate vaccines in mice, and also established that protection can be passively transferred to naïve mice by administering sera from mice immunized with conjugate. Mice were immunized with three doses of either 10 µg, 2.5 µg (full dose), 0.25 µg, or 0.025 µg S. Enteritidis COPS:FliC conjugate at 28 day intervals. Antibody titers to COPS and FliC measured by ELISA fell consonant with progressively smaller vaccine dosage levels; anti-FliC IgG responses remained robust at fractional dosages for which anti-COPS serum IgG titers were decreased. Nevertheless, >90% protection against intraperitoneal challenge was observed in mice immunized with fractional dosages of conjugate that elicited diminished titers to both FliC and COPS. Passive transfer of immune sera from mice immunized with the highest dose of COPS:FliC to naïve mice was also protective, demonstrating the role of antibodies in mediating protection. These results provide important insights regarding the potency of Salmonella glycoconjugate vaccines that use flagellin as a carrier protein.