If you give the flu to someone can you then catch it back off them?

I had the flu and gave it to my friend. I'm now all better but can I get the flue back off her?

Once you’ve had a particular strain of the virus, you’re permanently immune to it. The part that isn't so nice is that the viruses constantly transform themselves, so new strains make the rounds every year which is why new flu vaccines are created for each flu season.