If you have a limited supply the greater bang per buck would be to start with the young people who almost certainly haven't caught it yet and then work your way up.
Sure you are more likely to have it the older you are but even then you are unlikely to have all the strains. The vaccine covers like 9 or 10 different strains so it can protect you from the other strains even if you already have one of them.
It's generally only when you get into the 60s and up that the justification for not recommending the vaccine changes. Once you get into those later years the immune response changes a bit and you get new concerns.
An example being herpes zoster (chickenpox) where after a certain age you are recommended to get the shingles vaccine instead of the chickenpox vaccine since the way the disease presents and how the body reacts to it changes with age (technically shingles can happen at any age but generally herpes zoster presents as shingles instead of chickenpox the older you get).
If the underlying virus is the same, what is different between the vaccines? How it presents shouldn't matter as much?
Vaccines are subject to stringent safety standards since they’re administered to healthy people. The age limit may suggest that at the time of the recommendation, in the relevant jurisdiction, the manufacturer had not studied its safety and efficacy in >40 year olds.
(I also don’t think it’s an age limit as much as the upper end of a recommendation.)
And how can you say the vaccine definitely works for populations it hasn't been tested on?
There are two factors here:
1) Vaccine-derived immunity is a function of the individual's immune response, which in general, weakens significantly with age. It is not unrealistic for a vaccine to simply fail to elicit any response in someone old enough.
2) It is very, very difficult to recruit folks without HPV that are over 40 for a clinical trial. Most people of that age, who were never immunized, most likely have had it. This significantly convolutes the signal.
3) This is all especially confounded once something becomes "standard of care". Every year there are fewer and fewer people age 40+ with HPV.
For these reasons, the vaccine is currently officially ??? in people over 40. Most doctors will prescribe it anyways if you ask. It may or may not infer immunity. It almost certainly will not harm you.
https://www.cdc.gov/vaccines/vpd/hpv/hcp/recommendations.htm...
It's a level of evidence that's generated (usually) prior to ACIP, and it is presented to them, while there is not necessarily a bright line threshold.
Brilliant.
