That policy is a bit risky. That might diminish the use of other things that reduce significantly the spread of HIV, like condoms. It's still unknown how effective the gel is: maybe 90%, maybe 5%, condoms are 90% effective AFAIK[1].
Also, contraceptive success is usually annualized, like with correct condom use, pregnancy happens less than 3 percent per year. I assume there is a standardized level of sexual activity for that, too.
[1] http://www.advocatesforyouth.org/publications/416