Recombinant full-length Plasmodium falciparum circumsporozoite protein-based vaccine adjuvanted with GLA-LSQ: Results of Phase 1 testing with malaria challenge.

INTRODUCTION: Malaria is preventable yet causes >600,000 deaths annually. RTS, S, the first marketed malaria vaccine, has modest efficacy, but improvements are needed for eradication. METHODS: We conducted an open-label, dose escalation Phase 1 study of a recombinant, full-length circumsporozoite protein vaccine (rCSP) administered with adjuvant GLA-LSQ on days 1, 29, and 85 or 1 and 490 to healthy, malaria-naïve adults. Primary endpoints were safety and reactogenicity. Secondary endpoints were antibody responses and Plasmodium falciparum parasitemia after homologous controlled human malaria infection (CHMI). RESULTS: Participants were enrolled into four groups receiving rCSP/GLA-LSQ: 10 µg x 3 (n = 20), 30 µg x 3 (n = 10), 60 µg x 3 (n = 10) or 60 µg x 2 (n = 9); ten participants received 30 µg rCSP alone x 3; and six infectivity controls. Participants experienced no serious adverse events. Rates of solicited and unsolicited adverse events were similar among groups. All 26 participants who underwent CHMI 28 days after final vaccinations developed malaria. Increasing vaccine doses induced higher IgG titers, but did not achieve previously established RTS, S benchmarks. CONCLUSIONS: rCSP/GLA-LSQ had favorable safety results. However, tested regimens did not induce protective immunity. Further investigation could assess if adjuvant or schedule adjustments improve efficacy. TRIAL REGISTRATION: ClinicalTrials.gov Identifier NCT03589794.

Malaria prevention in children: an update.

PURPOSE OF REVIEW: Malaria cases and deaths decreased from 2000 to 2015 but remain increased since 2019. Several new developments and strategies could help reverse this trend. The purpose of this review is to discuss new World Health Organization (WHO) guidelines and recent research on malaria prevention in children. RECENT FINDINGS: Fifteen countries have now rolled out seasonal malaria chemoprophylaxis (SMC) in children at highest risk for severe malaria, and new WHO recommendations provide more flexibility for SMC implementation in terms of target age groups, geographic region, and number of cycles. Recent studies confirm that malaria burden in school aged children, and their contribution to transmission, is high. New guidelines permit expanded chemoprevention options for these children. Two vaccines have been approved for use in malaria endemic countries, RTS,S/AS01 E and R21/Matrix-M. Additionally, pyrethroid-chlorfenapyr bed nets are being deployed to combat resistant mosquitoes. SUMMARY: While challenges remain in malaria control towards elimination, new guidelines and recently approved vaccines offer hope. Monitoring for continued vaccine and chemoprevention effectiveness, and for possible epidemiologic shifts in severe malaria presentation and deaths as additional prevention efforts roll out will be paramount.

Factors associated with COVID-19 vaccination during June-October 2021: A multi-site prospective study.

INTRODUCTION: Vaccine hesitancy presents a challenge to COVID-19 control efforts. To identify beliefs associated with delayed vaccine uptake, we developed and implemented a vaccine hesitancy survey for the COVID-19 Community Research Partnership. METHODS: In June 2021, we assessed attitudes and beliefs associated with COVID-19 vaccination using an online survey. Self-reported vaccination data were requested daily through October 2021. We compared responses between vaccinated and unvaccinated respondents using absolute standardized mean differences (ASMD). We assessed validity and reliability using exploratory factor analysis and identified latent factors associated with a subset of survey items. Cox proportional hazards models and mediation analyses assessed predictors of subsequent vaccination among those initially unvaccinated. RESULTS: In June 2021, 29,522 vaccinated and 1,272 unvaccinated participants completed surveys. Among those unvaccinated in June 2021, 559 (43.9 %) became vaccinated by October 31, 2021. In June, unvaccinated participants were less likely to feel "very concerned" about getting COVID-19 than vaccinated participants (10.6 % vs. 43.3 %, ASMD 0.792). Among those initially unvaccinated, greater intent to become vaccinated was associated with getting vaccinated and shorter time to vaccination. However, even among participants who reported no intention to become vaccinated, 28.5 % reported vaccination before study end. Two latent factors predicted subsequent vaccination-being 'more receptive' was derived from motivation to protect one's own or others' health and resume usual activities; being 'less receptive' was derived from concerns about COVID-19 vaccines. In a Cox model, both factors were partially mediated by vaccination intention. CONCLUSION: This study characterizes vaccine hesitant individuals and identifies predictors of eventual COVID-19 vaccination through October 31, 2021. Even individuals with no intention to be vaccinated can shift to vaccine uptake. Our data suggest factors of perceived severity of COVID-19 disease, vaccine safety, and trust in the vaccine development process are predictive of vaccination and may be important opportunities for ongoing interventions.

Safety and immunogenicity of AGS-v PLUS, a mosquito saliva peptide vaccine against arboviral diseases: A randomized, double-blind, placebo-controlled Phase 1 trial.

BACKGROUND: Immunity to mosquito salivary proteins could provide protection against multiple mosquito-borne diseases and significantly impact public health. We evaluated the safety and immunogenicity of AGS-v PLUS, a mosquito salivary peptide vaccine, in healthy adults 18-50 years old. METHODS: We conducted a randomized, double-blind, placebo-controlled Phase 1 study of AGS-v PLUS administered subcutaneously on Days 1 and 22 at the Center for Vaccine Development and Global Health, Baltimore, MD, USA. Participants were block randomized 1:1:1:1:1 to two doses saline placebo, two doses AGS-v PLUS, AGS-v PLUS/ISA-51 and saline placebo, two doses AGS-v PLUS/ISA-51, or two doses AGS-v PLUS/Alhydrogel. Primary endpoints were safety (all participants receiving ≥1 injection) and antibody and cytokine responses (all participants with day 43 samples), analysed by intention to treat. FINDINGS: Between 26 August 2019 and 25 February 2020, 51 participants were enrolled and randomized, 11 into the single dose AGS-v PLUS/ISA-51 group and ten in other groups. Due to COVID-19, 15 participants did not return for day 43 samplings. Participants experienced no treatment-emergent or serious adverse events. All solicited symptoms in 2/10 placebo recipients and 22/41 AGS-v PLUS recipients after dose one and 1/10 placebo recipients and 22/41 AGS-v PLUS recipients after dose two were mild/moderate except for one severe fever the day after vaccination (placebo group). Only injection site pain was more common in vaccine groups (15/51 after dose 1 and 11/51 after dose 2) versus placebo. Compared to placebo, all vaccine groups had significantly greater fold change in anti-AGS-v PLUS IgG and IFN-É£ from baseline. INTERPRETATION: AGS-v PLUS had favourable safety profile and induced robust immune responses. Next steps will determine if findings translate into clinical efficacy against mosquito-borne diseases. FUNDING: UK Department of Health and Social Care.

Vaccine-induced seroconversion in participants in the North Carolina COVID-19 community Research Partnership.

Well-regulated clinical trials have shown FDA-approved COVID-19 vaccines to be immunogenic and highly efficacious. We evaluated seroconversion rates in adults reporting ≥ 1 dose of an mRNA COVID-19 vaccine in a cohort study of nearly 8000 adults residing in North Carolina to validate immunogenicity using a novel approach: at-home, participant administered point-of-care testing. Overall, 91.4% had documented seroconversion within 75 days of first vaccination (median: 31 days). Participants who were older and male participants were less likely to seroconvert (adults aged 41-65: adjusted hazard ratio [aHR] 0.69 [95% confidence interval (CI): 0.64, 0.73], adults aged 66-95: aHR 0.55 [95% CI: 0.50, 0.60], compared to those 18-40; males: aHR 0.92 [95% CI: 0.87, 0.98], compared to females). Participants with evidence of prior infection were more likely to seroconvert than those without (aHR 1.50 [95% CI: 1.19, 1.88]) and those receiving BNT162b2 were less likely to seroconvert compared to those receiving mRNA-1273 (aHR 0.84 [95% CI: 0.79, 0.90]). Reporting at least one new symptom after first vaccination did not affect time to seroconversion, but participants reporting at least one new symptom after second vaccination were more likely to seroconvert (aHR 1.11 [95% CI: 1.05, 1.17]). This data demonstrates the high community-level immunogenicity of COVID-19 vaccines, albeit with notable differences in older adults, and feasibility of using at-home, participant administered point-of-care testing for community cohort monitoring. Trial registration: ClinicalTrials.gov NCT04342884.

Risk of Severe Acute Respiratory Syndrome Coronavirus 2 Acquisition Is Associated With Individual Exposure but Not Community-Level Transmission.

BACKGROUND: Transmission rates after exposure to a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-positive individual within households and healthcare settings varies significantly between studies. Variability in the extent of exposure and community SARS-CoV-2 incidence may contribute to differences in observed rates. METHODS: We examined risk factors for SARS-CoV-2 infection in a randomized controlled trial of hydroxychloroquine as postexposure prophylaxis. Study procedures included standardized questionnaires at enrollment and daily self-collection of midturbinate swabs for SARS-CoV-2 polymerase chain reaction testing. County-level incidence was modeled using federally sourced data. Relative risks and 95% confidence intervals were calculated using modified Poisson regression. RESULTS: Eighty-six of 567 (15.2%) household/social contacts and 12 of 122 (9.8%) healthcare worker contacts acquired SARS-CoV-2 infection. Exposure to 2 suspected index cases (vs 1) significantly increased risk for both household/social contacts (relative risk [RR], 1.86) and healthcare workers (RR, 8.18). Increased contact time also increased risk for healthcare workers (3-12 hours: RR, 7.82, >12 hours: RR, 11.81, vs ≤2 hours), but not for household/social contacts. County incidence did not impact risk. CONCLUSIONS: In our study, increased exposure to SARS-CoV-2 within household or healthcare settings led to higher risk of infection, but elevated community incidence did not. This reinforces the importance of interventions to decrease transmission in close contact settings.

Low dose recombinant full-length circumsporozoite protein-based Plasmodium falciparum vaccine is well-tolerated and highly immunogenic in phase 1 first-in-human clinical testing.

Plasmodium falciparum circumsporozoite protein (CSP) is a major sporozoite surface protein and a key target of pre-erythrocytic malaria subunit vaccines. A full-length recombinant CSP (rCSP) based strategy could be advantageous, as this antigen includes a region critical to sporozoite cell attachment and hepatocyte invasion. The adjuvant Glucopyranosyl Lipid A-liposome Quillaja saponaria 21 (GLA-LSQ) functions as a TLR4 agonist, promotes antigen-specific TH1 responses and stimulates cytotoxic T cell production. To date, one study has reported the clinical acceptability of GLA-LSQ. We present interim results of a phase 1 first-in-human dose-escalation clinical trial of full-length rCSP vaccine given with or without GLA-LSQ adjuvant. Participants experienced only mild to moderate related solicited adverse events. The lowest adjuvanted vaccine dose achieved >90-fold rise in geometric mean anti-CSP IgG antibody titer. These favorable safety and immunogenicity results confirm the immunostimulatory capacity of this relatively new adjuvant and support next steps in clinical product development. Trial registration: ClinicalTrials.gov Identifier NCT03589794 (registered 18 July 2018).

Epitope-Specific Antibody Responses to a Plasmodium falciparum Subunit Vaccine Target in a Malaria-Endemic Population.

Circumsporozoite protein (CSP) coats the Plasmodium falciparum sporozoite surface and is a major malaria subunit vaccine target. We measured epitope-specific reactivity to field-derived CSP haplotypes in serum samples from Malian adults and children on a custom peptide microarray. Compared to children, adults showed greater antibody responses and responses to more variants in regions proximal to and within the central repeat region. Children acquired short-lived immunity to an epitope proximal to the central repeat region but not to the central repeat region itself. This approach has the potential to differentiate immunodominant from protective epitope-specific responses when combined with longitudinal infection data.

Serologic responses to the PfEMP1 DBL-CIDR head structure may be a better indicator of malaria exposure than those to the DBL-α tag.

BACKGROUND: Plasmodium falciparum erythrocyte membrane protein-1 (PfEMP1) antigens play a critical role in host immune evasion. Serologic responses to these antigens have been associated with protection from clinical malaria, suggesting that antibodies to PfEMP1 antigens may contribute to natural immunity. The first N-terminal constitutive domain in a PfEMP1 is the Duffy binding-like alpha (DBL-α) domain, which contains a 300 to 400 base pair region unique to each particular protein (the DBL-α "tag"). This DBL-α tag has been used as a marker of PfEMP1 diversity and serologic responses in malaria-exposed populations. In this study, using sera from a malaria-endemic region, responses to DBL-α tags were compared to responses to the corresponding entire DBL-α domain (or "parent" domain) coupled with the succeeding cysteine-rich interdomain region (CIDR). METHODS: A protein microarray populated with DBL-α tags, the parent DBL-CIDR head structures, and downstream PfEMP1 protein fragments was probed with sera from Malian children (aged 1 to 6 years) and adults from the control arms of apical membrane antigen 1 (AMA1) vaccine clinical trials before and during a malaria transmission season. Serological responses to the DBL-α tag and the DBL-CIDR head structure were measured and compared in children and adults, and throughout the season. RESULTS: Malian serologic responses to a PfEMP1's DBL-α tag region did not correlate with seasonal malaria exposure, or with responses to the parent DBL-CIDR head structure in either children or adults. Parent DBL-CIDR head structures were better indicators of malaria exposure. CONCLUSIONS: Larger PfEMP1 domains may be better indicators of malaria exposure than short, variable PfEMP1 fragments such as DBL-α tags. PfEMP1 head structures that include conserved sequences appear particularly well suited for study as serologic predictors of malaria exposure.

The Controlled Human Malaria Infection Experience at the University of Maryland.

Controlled human malaria infection (CHMI) is a powerful tool to evaluate the efficacy of malaria vaccines and pharmacologics. Investigators at the University of Maryland, Baltimore, Center for Vaccine Development (UMB-CVD) pioneered the technique in the 1970s and continue to advance the frontiers of CHMI research. We reviewed the records of 338 malaria-naive volunteers who underwent CHMI at UMB-CVD with Plasmodium falciparum from 1971 until 2017. These 338 volunteers underwent 387 CHMI events, including 60 via intradermal injection or direct venous inoculation (DVI) of purified, cryopreserved sporozoites. No volunteer suffered an unplanned hospitalization or required intravenous therapy related to CHMI. Median prepatency period was longer in challenges using NF54 (9 days) than in those using 7G8 (8 days), P = 0.0006 by the log-rank test. With dose optimization of DVI, the prepatent period did not differ between DVI and mosquito bite challenge (log-rank test, P = 0.66). Polymerase chain reaction (PCR) detected P. falciparum infection 3 days earlier than thick smears (P < 0.001), and diagnosis by ultrasensitive PCR was associated with less severe symptoms than smear-based diagnosis (39% versus 0%, P = 0.0003). Historical studies with NF54 showed a shorter median prepatency period of 10.3 days than more recent studies (median 11.0 days, P = 0.02) despite significantly lower salivary gland scores in earlier studies, P = 0.0001. The 47-year experience of CHMI at UMB-CVD has led to advancements in sporozoite delivery, diagnostics, and use of heterologous challenge. Additional studies on new challenge strains and genomic data to reflect regional heterogeneity will help advance the use of CHMI as supporting data for vaccine licensure.