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Chlamydia trachomatis is a Gram-negative obligate intracellular bacterium. It is the leading cause of bacterial sexual transmitted infections (STIs). World Health Organization figures estimated that over 90 million new cases of genital C. trachomatis infections occur worldwide each year. A vaccination program is considered to be the best approach to reduce the prevalence of C. trachomatis infections, as it would be much cheaper and have a greater impact on controlling C. trachomatis infections worldwide rather than a screening program or treating infections with antibiotics. Currently, there are no vaccines available which effectively protect against a C. trachomatis genital infection despite the many efforts that have been made throughout the years. In this paper, the many attempts to develop a protective vaccine against a genital C. trachomatis infection will be reviewed.

We have evaluated protection against a genital Chlamydia trachomatis infection in a pig challenge model. Protection was promoted by the porcine granulocyte macrophage-colony stimulating factor (GM-CSF), the Escherichia coli thermo-labile enterotoxin LT as an exceptionally potent mucosa-binding molecule and by a major outer membrane protein (MOMP)-based DNA vaccine carrying CpG motifs incorporated in the plasmid backbone. Protection achieved by mucosal (vaginal and nasal) immunization will be compared to systemic (intradermal) immunization. We could demonstrate that mucosal administration leads to significant protection against genital C. trachomatis challenge as significantly less severe macroscopic lesions, less chlamydial shedding and replication in the urogenital tract was demonstrated in the vaccinated animals. Also, significantly higher proliferative responses of peripheral blood lymphocytes were observed. Furthermore, the combination of nasal and vaginal immunization could induce serum antibody titers upon immunization and early upon challenge with C. trachomatis serovar E. However, the infection could not be eradicated. Systemic immunization was significantly less efficient at eliciting protection, which emphasizes the need for a mucosal vaccine in order to obtain significant protection against genital C. trachomatis infection.

Chlamydiaceae are Gram-negative obligate intracellular bacteria that can infect a broad range of animals and humans. Chlamydial infection of livestock, companion animals, and other animals may result in conjunctivitis, enteritis, pneumonia, abortion, rhinitis or arthritis but there is also a high incidence of apparently asymptomatic infections. Pigs can become infected by Chlamydophila pecorum, Chlamydophila abortus, Chlamydophila psittaci and Chlamydia suis (Everett et al., 1999). Chlamydial infections are nearly endemic in the Belgian pig population as 96% of the examined sera reacted positive in a recombinant major outer membrane protein (MOMP) antigen-based ELISA (Vanrompay et al., 2004). The purpose of this study was to examine the current serological status of our pig herd and to identify the chlamydial species involved in infecting Belgian pigs. At present, 193 (97%) of 200 examined farms tested positive for Chlamydiaceae-specific antibodies. We tried to identify the Chlamydiaceae species using a diagnostic platform comprising of culture, a Chlamydiaceae-species specific microarray and a PCR for the detection of the Chlamydia suis tetracyclin resistant gene tet(C). Our results were in accordance with the serological results, as Chlamydiaceae, and especially C. suis was highly prevalent in slaughtered pigs, in pigs ending up in the autopsy room of the Provincial Laboratory for the Prevention of Animals Diseases and in four different farms dealing with reproductive disorders. Furthermore, we could demonstrate C. suis in the eyes, the respiratory, the intestinal and the reproductive tract of sows and in semen samples of boars. We found no other species, with the exception of one Cp. pecorum and one Cp. abortus strain. In the present study, we demonstrated emerging tet(C) positive C. suis strains among Chlamydiaceae infections in pigs. Moreover, C. suis, for which Koch’s postulates have already been fulfilled in the past, are widespread in pigs throughout the world. Research towards the development of preventive measurements like probiotics (Pollmann et al., 2005) or vaccines should be promoted. In the future, the spread of tetracyclin resistant C. suis strains, for instance through international trading of boar sperm, should be carefully monitored as this may present a treat to human health.

Background In December 2020 the first European countries initiated their vaccination campaigns with the new COVID-19 vaccines. A cohort event monitoring study in seven European countries was initiated in order to monitor vaccine safety during the roll-out of these vaccines. Objectives The primary aim of the research described in this report is to generate (cumulative) incidence rates of patient-reported ADRs of COVID-19 vaccine brand in near real-time from the pooled European data for the first COVID-19 vaccine campaign in which participants received their first and second dose of the vaccine. This report describes the data available for pooling at the end of October 2021. Study design Participants were recruited, primarily at vaccination sites, in seven countries using three different web apps. Participants were required to fill in a baseline and at least one questionnaire related to adverse reactions. All solicited adverse reactions were coded automatically while unsolicited adverse reactions were coded manually. Serious adverse reactions, adverse events of special interest (AESI) and other reactions needing (medical) clarification were assessed by a qualified assessor. Results The most commonly reported systemic solicited reaction is fatigue which is closely followed by headache and malaise. The types of reported adverse reactions are comparable to the product information however the crude reporting rates varied. A total of 0.2% (0.114, 0.207) of adverse events were reported as serious after first dose; they were uncommon and comparable between the different vaccines, Rates were higher in Germany due to the inclusions of self reported seriousness. Nevertheless, rates of serious adverse reactions were low: 0.7% (0.678, 0.792). The frequency of reporting of AESI were comparable across vaccine brands: roughly 0.1-0.2% of all participants reported an adverse reaction which was considered an AESI. Conclusion The well-known, solicited adverse reactions were reported frequently while reporting of both serious adverse reactions and AESI were low. The initiated Early Covid Vaccine Monitor cohort event monitoring was challenging yet showed that an international collaboration is feasible. As additional (follow-up) data becomes available, further analysis on Covid-19 vaccine safety can be done., The research leading to these results was conducted as part of the activities of the EU PE&PV (Pharmacoepidemiology and Pharmacovigilance) Research Network (led by Utrecht University) with collaboration from the Pharmacovigilance Centre Lareb in the Netherlands. The project has received support from the European Medicines Agency under the Framework service contract nr EMA/2018/28/PE. This report expresses the opinion of the authors and may not be understood or quoted as being made on behalf of or reflecting the position of the European Medicines Agency or one of its committees or working parties. The work in this report is based on: EU PAS Register No: EUPAS39798