> can't vaccinate the boys to protect girls because that's not a direct benefit
Medical ethics doesn't allow a procedure which is good for society, but doesn't directly benefit the patient.
However, I think that is wrong. Elsewhere in society we frequently do that - for example we put people into prison, which is of very little benefit to the prisoner. We stand up to let an old person take a seat on a train, which is of no benefit to the person standing up. We send bailiffs, which is of little benefit to the debtor. We pay taxes, which is of little direct benefit to the taxpayer.
Why does the medical world have a stricter ethical standard when there are clearly benefits to society that cannot be realised because of the different approach?