Antiviral chewing gum to reduce influenza and herpes simplex virus transmission

Because approval involves evaluating a risk-benefit tradeoff, and the benefits for those groups are wildly different, as are the risk profiles, due to the way HPV strains[0] work. If they tested against a wide and heterogenous population from the start, it would risk demonstrating insufficient effect, which would eliminate the possibility of the vaccine for everyone. Instead, by testing against the group most likely to benefit from it (women, and specifically women of the age to have no prior exposure to HPV) they can see whether the vaccine has any potential at all, and expand from there.

As it turns out, the vaccine was incredibly effective for them, and as we studied it further, it turned out that other groups which had potentially lower benefits (men, older women) or higher potential risks (teenage girls) had a risk-benefit tradeoff that still overwhelmingly supported approval for those groups.

[0] yes, plural, because there are hundrends, and the vaccines (again, plural, because there are more than one) protect against a handful of them (although that fortunately includes the strains that account for 80-90% of HPV-caused cancers