It may be possible - according to a recently published article on HIV in the NEJM about the success of post-exposure prophylaxis for HIV. This means that you a take a pill (or a regimen of pills) very soon after possible exposure to the virus and it actually prevents the virus from invading your healthy cells. It's approved by the FDA for this purpose, standard procedure if a health worker is exposed while handling blood infected with HIV/AIDS and even covered by many insurance plans. Sounds like it should be as standard a procedure as putting your arm in a cast quickly after it's broken - so what's the catch?
*It's only available in San Francisco.
*It costs over $1,000/month without insurance.
*The CDC is really not into it (thinking it may actually encourage more risky behavior) so there's no federal funding for it right now.
For more information see this article in Mother Jones.