The feline three-way core vaccine is positioned against feline panleukopenia, herpesvirus and calicivirus, the baseline combination for most cats.

A four-way product adds protection against one further pathogen, and the exact ingredients vary by product. Read the label rather than judging by the number in the name.

More antigens is not automatically better: additional components raise immune load and the need to observe reactions, especially in kittens and frail cats.

Timing of the initial series, boosters and adult revaccination is set by a veterinarian based on age, lifestyle and local disease pressure.