Just because tons of Catholics do something doesn’t make it okay… tons of Catholics use ABC too. However, not necessarily saying that them having their children vaccinated is wrong, just pointing out the principle of the thing.
I’m not entirely sure about the vaccinations. Even if it was wrong, parents who didn’t know what it was made from (and I think that’s most of them) wouldn’t be sinning (like using asbestos in the days before it was discovered to be cancerous, of course it’s not your fault since how are you to know).
But I think that maybe using the vaccines is okay since it may be only remote material cooperation with the sin (ie, using the vaccines which someone else made and from which someone else again killed the baby, removes you a long distance from the sin of abortion - using the vaccine does not make you responsible for the death of the baby). Like I say, I’m not sure, maybe someone else can clarify.
The church doesn’t need medical knowledge in this case to determine if it is a sin. It is very simple. Oral sex by itself is a sexual act which is not procreative, like I said in my last post. They may not be using it as a means of contraception but it still is a means of contraception - like if a couple had sex with a condom on, not as contraception but to protect from AIDS (or even, if it was just once to see what it feels like), it would still be contraception and still be wrong. Or a man masturbating because he heard that it helps to prevent prostate cancer, still wrong. A sexual act must be procreative. Helping to procreate in a later sexual act (intercourse), doesnt make this first sexual act (OS) procreative.
If a natural means of aiding conception was found, and this natural means was not sinful, then of course it would be okay.
But we can’t do evil so that good may come out of it. In this case you need to consider the issue of what the couple is actually doing (the means), separate from their intent and the results of that act. When something is objectively a grave matter, such as OS, then it is still wrong whether you’re doing it just for fun, or for good reasons.