The purpose of a chlamydial vaccine is to prevent the sequelae of Ct infection: PID, infertility, ectopic pregnancy and blinding trachoma. An effective chlamydial vaccine could prevent primary infection, prevent re-infection, modify disease progression following
infection, or reduce transmission by reducing bacterial load or the duration of infection. Phase II studies could evaluate vaccine immunogenicity, safety and efficacy in preventing Ct infection in human volunteers. Human challenge experiments with Ct have not been reported since the ocular challenge studies more than 50 years ago, but urethral challenge studies in male volunteers may be possible; there is an extensive literature on urethral challenge of human volunteers with Neisseria gonorrhoeae. selleckchem The primary endpoint for phase III trials would probably be Ct infection. The frequency of sampling would need to be determined and, in the case of genital infection, treatment would need to be given as soon as infection SCH 900776 was detected. In the case of ocular infection in trachoma endemic communities this would not necessarily be the case, since the recommended control strategy is annual mass treatment of endemic communities or households. Phase IV trials could aim to evaluate vaccine efficacy in preventing PID,
but this would be particularly challenging, given the difficulty in making an accurate diagnosis. Improved diagnostic tests (biomarkers or imaging) will be needed. Evaluating efficacy in preventing infertility and ectopic pregnancy would require prolonged follow up and a large sample size. Phase IV trials
will be confounded by the necessity to treat subjects and their partners as soon as infection is diagnosed. Vaccine efficacy in preventing infection, or reducing inflammation, the duration of infection or the incidence and progression of scarring could be easily evaluated in a trachoma endemic community, by frequent examination of the subtarsal conjunctiva. The incidence and progression of conjunctival scarring can be determined using an ocular microscope (slit lamp). Our recent studies have shown that confocal microscopy can identify conjunctival scarring out at an early stage, before it is clinically apparent . The evidence from trachoma vaccine trials in monkeys and humans has been interpreted as showing that vaccination can lead to more severe inflammatory disease following re-challenge with a different serovar of Ct As discussed above, the evidence for this from human trials is not convincing; and in the only vaccine trial in which scarring was included as an endpoint, its prevalence was reduced in the vaccinated group. Nevertheless, the spectre of an immunopathological response to chlamydial vaccination will not be easily laid to rest.