Titers after 2 polio vax's?

[tbone]

Ds4 has had 2 polio vaccines over a year ago.  Do you all know if it would be likely for him to have a positive titer?  If so, I'd like to skip the third.  I don't want him to not be completely unprotected as we do travel to areas that still have polio problems.  He scheduled for his annual physical this week and I'm sure the topic will come up with his doc.

Thanks!