Why are some vaccines so age specific?

This thread reminded me of a long-standing question: Whay are certain vaccines so age-specific? Like the new HPV vaccine that is only for children, and the shingles vaccine I can’t have yet.

I’m a firm beliver in educating my immune system at every opportunity; why am I being discriminated against?

HPV: After a certain age, you’ve probably already been exposed to one or more of those strains.

You can’t get the shingles vaccine because they haven’t tested it on people younger than 50 so they don’t know if it will be effective enough to warrant the effort.

BTW, I was able to get the HPV vaccine as an adult, and there has been some discussion about having more adults vaccinated against it. But yes, for many adults, they would probably be already exposed (and immune) to the strains it protects against.

Many vaccines are age-specific because the diseases they protect affect that population segment worse than other segments. Other age groups are either not affected, less severely affected, or with other treatment options available other than the vaccine.

The HPV vaccine isn’t only for children, unless there’s a really new kids-only version I haven’t heard of yet. It’s recommended for young women up through age 26, but there’s not a firm cut-off – I had it when I was 27. I asked my doctor about the age recommendation and he said there was no reason I couldn’t have the vaccine, it was just that if a woman makes it to her late 20s without picking up HPV then she’s probably not at a high risk of getting it. However, the vaccine has not been tested on older women, so if I’d been farther from the recommended age then my doctor might have expressed some concerns about unknown health risks.

And there would be no reason to motivate them to do so. The shingles vaccine is just a double dose of the chicken pox vaccine. Those who had the chickenpox vaccine, which includes much of the population younger than 17, won’t be targets for it as they age. Those younger than 50 but older than 17 are currently at lowish risk of shingles before 50 and most will age into 50 (so Merck will make their money). Given the low incidence of shingles before 50 the study would need to be very large to get enough cases without an extremely long follow up period. Either way, an expensive study for little gain.

HPV is indeed based on the concept that giving to populations who statistically may already be infected makes little sense. Those with more partners are at greatest risk and those with more partners tended to start younger than 26.

Of course there was the Mom in practice who while discussing the vaccine for her child, questioning the age cut-off, and whether to give it at 11 or wait until her child was closer to at-risk behaviors, volunteered that in her teens and 20’s she had very little risk - her now ex-husband had been, at marriage, her first and only partner, but that now, well over 26 and relatively recently divorced, she’d benefit more. (Thus the no way to know for sure how long it will last was possibly relevant … maybe her daughter might not be at risk until late 30’s and beyond too.)

Some do not induce protection until a child’s immune system is more developed.

In Spain at least, part of the cutout age is linked to the assumption that “anybody who’s had sex will have picked HPV”, combined with “anybody over age X has had sex” and a “don’t ask in front of their mothers, don’t believe what they say anyway” attitude about virginity on the part of the crowd which has the second assumption. SiL, a GP, had some arguments along the lines of “what do you mean, any girl over 17 [the original cut-off age here] will have had sex? I got married at 25 and I was a virgin! And if you plan on calling me a liar remember I know how to use a scalpel!”

The cutoffs are more along the lines of “we recommend that people in X age range have it”, as they’re less likely to have the bug already (HPV), or because they’re considered high-risk when other people aren’t (flu, shingles).