Kitten has second URI - FHV-1?

[AnsonA4]

Our new kitten developed a URI at 7 weeks and of course we took him to the vet and he was put on l-lysine and antibiotics. He got better in about a week, not before infecting our 7 year old cat even though he was quarantined.

Now, about 1 month after his symptoms disappeared, he is showing signs of a URI again, runny nose, glazed eyes, lethargy. The 7 year old seems okay for the time being.

The kitten has not had any contact with any other animals other than the 7 year old cat. He has a vet appointment for boosters this week anyway but I was hoping someone could provide some insight.

Is it the herpes virus? Does this mean he is a carrier since he hasn't had any contact with another animal? Could it be something simple like an allergy? Is l-lysine actually helpful - I've read it can cause more harm than help even:
http://avmajournals.avma.org/doi/abs...jvr.70.11.1391

Thank you all so much in advance for any insight!

Here is Ziggy and Maya: