In one of the most highly publicised statements, in October 2003, the President of the Vatican's Pontifical Council for the Family, Cardinal Alfonso Lopez Trujillo, said: "The AIDS virus is roughly 450 times smaller than the spermatozoon.The spermatozoon can easily pass through the 'net' that is formed by the condom.The evidence we have is based on three types of trials, and each has potential weaknesses.
For the reasons described above, there is a convention to use two different words when describing the effect of prevention interventions.
Research early on in the epidemic showed that 40 to 70% of men who claimed they use condoms 100% of the time in fact did not use them for every act of intercourse.
Twenty years later, 51 to 66% of women taking part in a microbicide study reported 100% condom usage at different time points during the trial, but the researchers calculated from inconsistency in their answers that the actual proportion who maintained 100% condom use was 25%.
Consistently used condoms provide significant protection against HIV, pregnancy and sexually transmitted infections (STIs).
The degree of protection they offer against HIV and STIs is significantly better than any other single prevention method, taken in isolation, other than sexual abstinence or complete mutual monogamy between two people who have tested negative for HIV.