To not understand the logic in this statement on vaccination

[Jarstastic]

DSS13 in year 8 is to go for an HPV vaccination (at his school but in a drive through) this week.

Fantastic I thought, been thinking about HPV vaccinations for boys (in society) for a few years. I wondered if he was the first year so looked up online. I found this article that he is the second year.

www.bbc.co.uk/news/health-49522669

In response to people asking for it to be available for older boys on request, I don’t understand the govt stance at the end.
“Extending the vaccine to boys aged over 13 would only have a limited benefit as older boys and young men are already protected by herd immunity - built up by 10 years of the girls' successful vaccination programme.”

I’m totally baffled. Why are say 15-year olds in a position through herd immunity. If that’s the case doesn’t that undermine the case for the 13-year olds having the vaccine? (Isn’t the point as well as protecting boys it would help with herd immunity for the girls just like the MMR vaccine for boys and girls eradicating rubella in the UK?)

Can someone please explain it to me? I

A complete guess here but I assume that the thinking is most 13 year old boys aren’t having sex until they’re older so that’s why? It doesn’t make sense to me either!

Because a generation of girls/young women now have immunity, which means they won't spread it to/from anyone they have sex with, so it doesn't matter as much if the boys their age are retrospectively done from a public health point of view.

But then older adults aren't done either, so you might as well say we should all be offered it (more so, in fact, as half of us haven't been).

Same sex relationships are the main difference it will make, vaccinating boys too. Gay and bi men up to 45 are being offered it.

Of course they are also assuming that people generally have sex with people fairly close to their age, otherwise a younger man could catch it from an older woman.

What I mean is, it's much easier to just add boys to the current schedule than also do a catch-up programme, so the cost (both financial and practical) isn't worth it as that age group is already largely protected because the girls are, and any gay/bi boys can have it anyway.