There are many reasons why the circumcision clinical trials will most probably not necessarily translate to real world effects.
1. The clinical trial effects are too low, a 50% clinical effect leads to low population level protection. French researcher Garenne, demonstrated that clinical effects do not always translate to Population effects (Major reason being size of clinical effect), and that past research had shown that vaccinations that had a 50% clinical effect had virtually zero population effects.
2. Men will adapt their behaviour to make up for circumcision. Whatever loss of sensation men experience, will be made up for in adaptation of behaviours and this could mean, more frequent sex, more vigorous sex, although speculative there could be more varied sex including the possibility of anal intercourse, more sex partners, less condom use, less safe sex behaviour.
3. The trials were ended early exagerrating clinical effects.
4. The real world wont have the same levels of clinical support, clinical efficacy, and education that the clinical trials had.
5. Relative risk reduction and episodic protection is not life long protection, or absolute risk protection.
6. Women appear to be infected at 50% higher rates when having sex with a circumcised man. This may be due to resuming sex too early before wound has healed, more vigourous sex or more frequent sex to compensate for loss of foreskin.
7. Trials demonstrated high internal reliability, but little evidence of external validity, which appears quite low when examining populations. Garenne found that certain populations of circumcised men have higher rates of HIV infections, than non-circumcised populations in certain African Nations.
8. There may now be a greater reliance of circumcison than wearing condoms and practising safe sex.
9. No emphasis was made on addressing the major cause of high population infection rates, namely high levels of promiscuity, high numbers of sex partners, and it is this cultural behavioiural phenomena which requires, massive culture change.
10. The trials were not double blinded the reserachers knew who were in the circumcised group, and the circumcised group received more attention, time, education, and emphasis on wearing condoms.
11. The USA which has the highest circumcision rates in the western world, and also the highest rates of HIV & STI's in the western world. Studies that examined the differences noted Americans tended to have a higher number of sex partners and used less condoms than their European peers. This may be that American men who are circumcised adapt their behaviours to compensate for lack of foreskin, or other factors may be contributing, such as cultural sexual practices. What it does demonstrate is that an increase in unsafe sex behaviours eliminates any protective effect that may be evident in a clinical trial setting.