I haven't heard it before... you should be in sure about that. May I ask you to show me a reference?

Hi, is this the poem do you mean? I caught the happy virus last night When I was out singing beneath the stars. It is remarkably contagious - So kiss me. As the other friends said it's not from Hafiz(Hafez), but I translated for you: I caught the happy virus last night شب گذشته ویروس شادی گرفتم When I was out singing beneath the stars. آنگاه که در زیر آسمان آواز می خواندم It is remarkably contagious - So kiss me. شدیدا واگیردار (مسری) است، پس مرا ببوس اینجا منظور شاعر اینه که: این حال خوشی و شادی که بر اثر ویروس شادی وارد بدنش شده است نوعی بیماری مسری(واگیردار) است، پس به معشوقش میگوید که او(شاعر یا مریض) را ببوسد تا وی(معشوق) نیز سرخوش و خوشحال شود

Hi. It is not a poem written by Hafiz. I found the source and have no idea what does the name hafiz do there under the poem. But it seems the poet's name is Hamad. Here is the link. You can ask him to explain you. hellopoetry.com/hamad I guess it is an unduly free translation of one of Hafiz's poems, a free translation in a way I cannot tell what is the original poem.

Hafiz lived in 14th century, so I'm pretty sure that back then people didn't know what a virus is. There is either something wrong with the translation or this is not from Hafiz at all.