Consistent condom use A population may

transmission during penetrative sex by about 90%. Thus, the best
estimate that may be deduced from all these studies is that condoms
used correctly and consistently reduce the risk of transmission by
about 90%. With perfect use, effectiveness may be even higher,
though not 100%.
It is important to clarify that an effectiveness of 90% does not mean
that HIV transmission will take place in 10% of sexual acts where
condoms are used. In fact, the risk of transmission is much lower.
If the risk of sexual transmission is one in 500 without a condom, it
would be reduced to one in 5000 when a condom is used.Consistent condom use
A population may use large numbers of condoms but the impact will
be limited if the persons who use them most do not do so consistently.
There is little evidence that using condoms sometimes (but not always)
provides any greater protection than not using condoms at all. In fact,
one study from Uganda found that individuals who sometimes used
condoms were at higher risk of infection than those who never used
them, perhaps because they were more risky in other aspects of their
sexual behaviour, such as the number of partners they had 17.
In analysing overall data on condom use, it is critical to determine who
is using condoms. In a situation where overall condom use in general
is high, but condom use is low in those few encounters where it could
make a measurable difference, condom promotion must become more
focused. This could occur, for example, if those at highest risk of HIV
infection have lower rates of condom use, while people at low risk
have higher rates of condom use.