Epidemiological impact of a syphilis vaccine: a simulation study

Syphilis vaccine development: Aligning vaccine design with manufacturing requirements

Syphilis, caused by Treponema pallidum subsp. pallidum, is a global health concern with increasing rates worldwide. Current prevention strategies, including screen-and-treat approaches, are not sufficient to resolve rising infection rates, emphasizing the need for a vaccine. Developing a syphilis vaccine necessitates a range of cross-disciplinary considerations, including essential disease-specific protection, technical requirements, economic feasibility, manufacturing constraints, public acceptance, equitable vaccine access, alignment with global public vaccination programs, and identification of essential populations to be vaccinated to achieve herd immunity. Central to syphilis vaccine development is prioritization of global vaccine availability, including access in low- to middle-income settings. Various vaccine platforms, including subunit, virus-like particle (VLP), mRNA, and outer membrane vesicle (OMV) vaccines, present both advantages and challenges. The proactive consideration of both manufacturing feasibility and efficacy throughout the pre-clinical research and development stages is essential for producing an efficacious, inexpensive, and scalable syphilis vaccine to address the growing global health burden caused by this disease.

Public willingness to receive chlamydia, gonorrhea, syphilis, and trichomoniasis vaccines: a scoping review

BACKGROUND

Sexually transmitted infections (STIs) like chlamydia, gonorrhea, syphilis, and trichomoniasis contribute significantly to global morbidity and mortality. Researchers are pursuing vaccines for these STIs, and a clinical trial is currently underway for a chlamydia vaccine. However, there is little research available on individuals' willingness to receive chlamydia, gonorrhea, syphilis, and trichomoniasis vaccines. The purpose of this analysis was to map the existing literature we have on individuals' willingness to receive these bacterial/parasitic STI vaccines and understand what information on vaccine acceptability is still needed.

METHODS

We searched seven databases for literature on STI vaccine acceptability, then conducted title/abstract and full-text reviews to assess eligibility. All reviews and abstractions were conducted blindly by two reviewers, with discrepancies settled by discussion or the input of a third reviewer.

RESULTS

Eight of the original 2,259 texts of interest met inclusion criteria. After data abstraction, we found that gonorrhea was the most commonly examined, followed by chlamydia and syphilis. Trichomoniasis vaccine acceptability was not reported. Most texts reported high acceptability, but there did not appear to be data describing how vaccine characteristics affect acceptability. Similarly, while the literature covers a variety of populations, most of the study populations were based out of the United States or Canada and were patrons of healthcare facilities or participants from a larger health intervention study. Therefore, more information is needed on populations outside North America, and on groups with lower healthcare access and utilization.

CONCLUSION

As the incidence of bacterial and parasitic STIs increase, and as we grow nearer vaccines for these illnesses, understanding how likely the public is to accept and receive these vaccines is crucial to their success. While the existing literature describes STI vaccine acceptability in a variety of populations, their overall number is small. More research into STI vaccine acceptability outside of North America, and especially examining how factors like number of doses, timing, and cost influence vaccine acceptability is needed to ensure effective future vaccine rollouts.

Notes on syphilis vaccine development

The quest for a syphilis vaccine to provide protection from infection or disease began not long after the isolation of the first Treponema pallidum subspecies pallidum (T. pallidum) strain in 1912. Yet, a practical and effective vaccine formulation continues to elude scientists. Over the last few years, however, efforts toward developing a syphilis vaccine have increased thanks to an improved understanding of the repertoire of T. pallidum outer membrane proteins (OMPs), which are the most likely syphilis vaccine candidates. More has been also learned about the molecular mechanisms behind pathogen persistence and immune evasion. Published vaccine formulations based on a subset of the pathogen's OMPs have conferred only partial protection upon challenge of immunized laboratory animals, primarily rabbits. Nonetheless, those experiments have improved our approach to the choice of immunization regimens, adjuvants, and vaccine target selection, although significant knowledge gaps remain. Herein, we provide a brief overview on current technologies and approaches employed in syphilis vaccinology, and possible future directions to develop a vaccine that could be pivotal to future syphilis control and elimination initiatives.

Strategies for successful designing of immunocontraceptive vaccines and recent updates in vaccine development against sexually transmitted infections - A Review

Background

Objective

Methods

Results

Conclusion

The effect of public health awareness and behaviors on the transmission dynamics of syphilis in Northwest China, 2006-2018, based on a multiple-stages mathematical model

Syphilis, a sexually transmitted infectious disease caused by the bacterium treponema pallidum, has re-emerged as a global public health issue with an estimated 12 million people infected each year. Understanding the impacts of health awareness and behaviors on transmission dynamics of syphilis can help to establish optimal control strategy in different regions. In this paper, we develop a multiple-stage SIRS epidemic model taking into account the public health awareness and behaviors of syphilis. First, the basic reproduction number R0 is obtained, which determines the global dynamics behaviors of the model. We derive the necessary conditions for implementing optimal control and the corresponding optimal solution for mitigation syphilis by using Pontryagin's Maximum Principle. Based on the data of syphilis in Ningxia from 2006 to 2018, the parameterizations and model calibration are carried out. The fitting results are in good agreement with the data. Moreover, sensitivity analysis shows that the public awareness induced protective behaviors C_e, compliance of condom-induced preventability ε and treatment for the primary syphilis m₁ play an important role in mitigating the risk of syphilis outbreaks. These results can help us gain insights into the epidemiology of syphilis and provide guidance for the public health authorities to implement health education programs.

Estimating the syphilis incidence and diagnosis rate in Japan: a mathematical modelling study

OBJECTIVES

The reported number of syphilis cases is increasing in Japan. In this study, we aimed to estimate both the incidence of infection and diagnosis-and-reporting rate using a mathematical model that captures the time course of infection.

METHODS

We analysed yearly notification data from 1961 to 2016 and stratified according to clinical stage and sex. We built a compartmental ordinary differential equations model to describe the natural epidemiological course of syphilis in which the incidence of infection and diagnosis-and-reporting rate were included as time-varying parameters that we estimated via the maximum likelihood method.

RESULTS

From 2008 to 2016, the estimated number of new syphilis cases among men and women was 1070 (95% CI 1037 to 1104) and 302 (95% CI 287 to 318), respectively, which was increased from the previous period (1999-2007) with 269 (95% CI 256 to 282) and 71 (95% CI 64 to 78) cases, respectively. The diagnosis-and-reporting rate did not vary greatly over time. We estimated the number of undiagnosed syphilis cases from either incubating or early clinical (ie, primary or secondary) infections in 2016 to be 262 (95% CI 249 to 275) and 79 (95% CI 74 to 84) for men and women, respectively.

CONCLUSIONS

The recent increase in reported cases of syphilis is owing to an increase in the number of infections. We found no evidence of time-dependent improvement in detection or reporting.

Syphilis Vaccine Development: Requirements, Challenges, and Opportunities

Syphilis, caused by the spirochete Treponema pallidum subspecies pallidum, continues to be a prevalent disease in low- and middle-income countries, and has reemerged in key populations, including men who have sex with men, in high-income nations. The rising number of cases shows that syphilis elimination will require augmentation of public health screening and treatment campaigns with syphilis vaccine development and implementation initiatives. Optimal vaccine candidates, deciphered from careful consideration of the pathogenic mechanisms used by T. pallidum, will need to be paired with appropriate human-track adjuvants designed to elicit the correlates of protection needed to prevent infection/disease. This article provides an overview of the development pipeline customized for a syphilis vaccine, including the preferred product characteristics, the investment case, and a proposed vaccinogen selection strategy outlining the essential qualities that need to be targeted by a syphilis vaccine.

Increased Syphilis Testing of Men Who Have Sex With Men: Greater Detection of Asymptomatic Early Syphilis and Relative Reduction in Secondary Syphilis

Background

Syphilis rates have increased markedly among men who have sex with men (MSM) internationally. We examined trends in syphilis testing and detection of early syphilis among MSM in Australia.

Methods

Serial cross-sectional analyses on syphilis testing and diagnoses among MSM attending a national sentinel network of 46 clinics in Australia between 2007 and 2014.

Results

359313 clinic visits were included. The proportion of MSM serologically tested for syphilis annually increased in HIV-negative (48% to 91%; Ptrend < .0001) and HIV-positive MSM (42% to 77%; Ptrend < .0001). The mean number of tests per man per year increased from 1.3 to 1.6 in HIV-negative MSM (Ptrend < .0001) and from 1.6 to 2.3 in HIV-positive MSM (Ptrend < .0001). 2799 and 1032 syphilis cases were detected in HIV-negative and HIV-positive MSM, respectively. Among HIV-negative MSM, the proportion of infections that were early latent increased from 27% to 44% (Ptrend < .0001), while the proportion that were secondary decreased from 24% to 19% (Ptrend = .030). Among HIV-positive MSM, early latent infections increased from 23% to 45% (Ptrend < .0001), while secondary infections decreased from 45% to 26% (Ptrend = .0003). Among HIV-positive MSM, decreasing secondary syphilis correlated with increasing testing coverage (r = -0.87; P = .005) or frequency (r = -0.93; P = .001).

Conclusions

Increases in syphilis screening were associated with increased detection of asymptomatic infectious syphilis and relative falls in secondary syphilis for both HIV-positive and HIV-negative MSM nationally, suggesting interruption of syphilis progression.

The current status of syphilis prevention and control in Jiangsu province, China: A cross-sectional study

Objective

To analyze the midterm evaluation data from the National Syphilis Prevention and Control Plan (2010–2020) and evaluate the current status of syphilis prevention and control in Jiangsu province, China.

Methods

We collected data via (1) field surveys conducted in 2015 and (2) data recorded in existing syphilis surveillance systems. We conducted descriptive statistical analysis to evaluate the current landscape of syphilis control initiatives and their potential effect in syphilis control.

Results

The incidence of all cases of syphilis decreased from 2010 (32.3 per 100,000) to 2015 (30.1 per 100,000), with an annual growth of -1.17% (x²_trend = -7.52, P<0.001) in Jiangsu province. The incidence of primary and secondary syphilis and congenital syphilis both decreased significantly from 2010 to 2015. The average awareness rate of syphilis knowledge among professional personnel was 95.4% (3781/3963). Rural residents had the lowest awareness rate (83.5%, 1875/2245) and commercial sex workers had the highest awareness rate (92.1%, 7804/8474) in 2015. Only 47.8% (33908/70894) of patients received provider-initiated syphilis counseling and testing (PISTC) services in sexually transmitted disease (STD) clinics, but 94.5% (87927/93020) of all syphilis patients received free testing for syphilis. Overall, 97.2% (9378/9648) of syphilis reported cases of syphilis at medical institutions were confirmed to be accurate, and 92.2% (5850/6345) of patients diagnosed with syphilis at medical institutions received treatment with penicillin.

Conclusion

The syphilis incidence rate in Jiangsu has decreased in recent years, but remains at a high level. It is essential to promote PISTC services to improve knowledge of syphilis and rates of testing and treatment in Jiangsu province.