Final answer:
Herpesvirus and calicivirus are the two most common agents involved in feline respiratory disease complex for which vaccines exist. These viruses are highly contagious and can cause serious diseases in cats, making vaccinations crucial for feline health.
Step-by-step explanation:
The Most Common Agents in Feline Respiratory Disease Complex. The two most common agents involved in feline respiratory disease complex for which vaccines exist are herpesvirus and calicivirus. These viruses are capable of causing severe respiratory infections in cats and are highly contagious. Vaccines have been developed to protect cats from these diseases, which can have serious or even fatal complications if not appropriately managed. It's crucial for pet owners to be aware of these potential threats and to ensure their cats receive the necessary vaccinations to maintain their health.