Given Texas's conscientious objector exemption, the vaccine seems not to be really mandatory. (I say "seems" because I'm not positive how the exemption, which is on its face very broad, is applied in practice.) But what if it were mandatory? Should we oppose that on broadly libertarian grounds? When I say "we," I'm referring not just to hard-line libertarians (of which I'm not one) but also to those who have general Millian "free to do what I please so long as I don't hurt others" sympathies, even if those sympathies can sometimes be trumped by other concerns.

My tentative sense is that immunizations against communicative diseases are often quite proper, even as a libertarian matter. I say "tentative" because I'm sure others have thought about the subject in much more depth than I have, and perhaps they can prove me mistaken. But let me quickly lay out my thinking.

It is a sad fact of biology that we can spread communicable diseases without any conscious decision on our parts, even without knowing that we are infected. Any time we do this, we are indirectly causing harm to someone else. Say Alan has sex with Betty, who then has sex with Carl, who then has sex with Denise; say Alan is infected with HPV, and each sexual act would (absent immunization) spread HPV; and say Betty isn't immunized against HPV. Betty's failure to get immunized would lead to her unwittingly spreading the virus, which ends up hurting Denise. She hasn't intentionally harmed Denise, but she has harmed her -- you might categorize the harm as negligent (in that it flows from negligent failure to get immunized) or not, but it is indeed the infliction of harm.

Now it's true that the harm also flowed from Denise's voluntary decision to have sex with Carl. But, as I noted in an earlier post, it's hard to see why this should excuse the harm caused by Betty, any more than Denise's voluntary decision to get on the road excuses the harm that someone imposes on Denise by crashing into her with a car (or, if you prefer, that Betty imposes on Denise by crashing into Carl's car, which then crashes into Denise's).

Even if you think that some people's having many sexual partners should affect the analysis, remember that HPV can be spread even among people who are about as sexually constrained as can be expected. The Alan-Betty-Carl-Denise connection can happen even if Betty was a virgin when she married Alan; if she then didn't have sex with Carl until she married him (assume Alan had died, or had left Betty); and if Denise was a virgin when she married Carl (again, assume Betty had died, or had left Carl). This very scenario might be rare -- but lots of other scenarios in which people had led fairly safe lives, but find themselves getting HPV, are also quite plausible. And more broadly, even if people are leading somewhat riskier lives than this, participating in spreading a disease to them may still be quite rightly seen as harming them, despite their own role in choosing risky behavior.

Of course, if HPV immunization were 100% reliable, and 100% available, then this analysis wouldn't apply with quite the same strength: Presumably any person who remains at risk of HPV infection would be at risk because of her own refusal to get the vaccine. Yet while the immunization is supposed to be extremely reliable for 9-to-26-year-olds, it hasn't been tested on over-26-year-olds, and thus isn't recommended for them. Moreover, some people won't get the vaccine, possibly because they can't afford it. ($360 isn't chopped liver for many, especially for people who aren't in America.) Even an "assumption of risk" presumptive libertarian may reasonably conclude, I think, that refusing to get immunized is wrongful behavior, because it may lead to one's becoming a vehicle for transmitting a dangerous and sometimes deadly disease to third parties, and thus harming those third parties (in a way that an "assumption of risk" argument would not excuse).

Finally, recall that the question here is whether to immunize girls who are under 18, girls who may well get infected before 18 if the immunization is delayed until then. Even if it was just their own health on the line, and not the health of others whom they might indirectly infect, we could rightly say that they don't have the maturity to refuse this protection, and that their parents shouldn't be entitled to refuse this protection on their behalf. But since the question of what kinds of modest physical risks parents should be free to have their children run is thorny, contested, and old hat enough that I'm not sure I can add much to the subject, I thought I'd focus primarily on how parents' refusal to immunize their daughters may hurt others, and not just the daughters themselves.

So a brief summary: There may well be practical problems with truly mandatory immunization, and it may well be that herd immunity would mean that 90% immunization is good enough to reduce the risk to a level that doesn't merit regulation. There may of course also be practical objections to immunization if the immunization seems unduly risky (a question I set aside in the first post in this chain). But as a moral matter of individual liberty, it seems to me that there's little support for a claimed freedom from getting immunized -- and especially a claimed freedom from getting your underage children immunized. A requirement that people not allow their bodies to be media for unwitting transmission of deadly diseases strikes me as quite compatible with a generally libertarian perspective on the world.