True. Not a single condom gives a 100% guarantee of protection, both against various STDs and against unwanted pregnancy. This is primarily due to the factors of marriage and misuse (the condom breaks or slips during PA).
Speaking specifically about HIV, the statistics of condom use (the highest quality Durax, Contex) tell us about 98-99 % of the percentage of protection against STDs, including HIV. Speaking specifically about HIV, the probability of contracting em with PA without a condom is different for women and for men, so for women it is about 3 times higher, and, on average, 15% with a single, unprotected PA. For men this figure is on average about 5%.
By simple calculations we get about 0.00225%
That is, on average, approximately one case in 2250 PAs using a condom for women and one in 7500 for men. The probability is certainly small, but there is.
Let's put together what we know about condoms.
Condoms are usually made from latex. Pores are present in latex. Their diameter can be up to 5 microns. And the diameter of the HIV virus is 0.1 micron. And what follows from this? ..
Yes, nothing follows. Because in this equation, we forgot to take into account the thickness of the condom wall - and it is about 60 microns. Once again: in the wall of a condom as much as 60 microns thick, there are pores with a diameter of only 5 microns. That is, if the virus gets into such a time, then it will not jump out on the other side of the condom, but will only be inside the pore. With the longed for freedom, it will be shared by another 55 microns of latex.
In addition, do not forget about the lubricant that covers the condom - it also plays against viruses, filling the pores and making it difficult to move through them.