Can someone reassure me- someone kissed my baby 😫

So I have been very protective of my LO. He’s 4 months today. I’m very open about no kissing, don’t touch him if you’re sick, etc. well I finally started letting family hold him. And someone kissed the back/side of his head. I think I saw a cold sore on her lip and I am literally freaking out. I said “oh no kissies please” in a nice way and she nodded. I didn’t want to make her feel any worse than I’m sure she already did but I just wanted to cry. No one else is holding him for the rest of the year. Can someone please reassure me of this 😔 all I can think of is meningitis.