Core vaccines, and why puppies and kittens need a series

Vaccination is the single most effective thing you can do to protect a young pet, and the schedule is not arbitrary. Puppies and kittens are born with antibodies from their mother, passed in the first milk, which protect them for the first weeks of life — but those same antibodies also block vaccines, so a single shot given too early does nothing. The solution is a series of shots three to four weeks apart, from six to eight weeks through to fourteen to sixteen weeks: as the maternal antibodies fade, one of the shots in the series will take hold and produce lasting immunity. That is why the schedule has three rounds, and why it matters to complete all of them — a puppy that has had one shot is not protected, it is halfway through a process.

The core vaccines for dogs are DHPP — distemper, hepatitis (adenovirus), parvovirus and parainfluenza — usually given as a single combined injection, plus rabies, which is required by law in most places. The core vaccines for cats are FVRCP — feline viral rhinotracheitis (herpesvirus), calicivirus and panleukopenia (feline distemper) — plus rabies. These are called "core" because every dog and cat needs them, whatever its lifestyle, because the diseases are widespread, serious and often fatal. Non-core vaccines — bordetella (kennel cough), leptospirosis, Lyme disease, canine influenza for dogs, and feline leukaemia virus (FeLV) for cats — are given only when the risk justifies them: a dog that goes to daycare needs bordetella, a dog that swims in rural water may need leptospirosis, and a cat that goes outdoors may need FeLV.

The schedule in detail

At six to eight weeks, the first DHPP or FVRCP. At ten to twelve weeks, the second, plus leptospirosis for dogs if recommended in your area, and FeLV for at-risk kittens. At fourteen to sixteen weeks, the third, plus rabies. At twelve months, a booster of the core vaccines and a rabies booster. After that, core vaccines are boosted every one to three years, depending on the vaccine and your vet's protocol — many modern vaccines are licensed for three years, but rabies timing is set by law and varies by location. The helper on this page shows the next step for your pet's age, and the full timeline, so you can see where you are in the series and what comes next.

Socialisation and the vaccination gap

The vaccination series creates a dilemma: the socialisation window, when a puppy learns what is normal and safe, runs from about three to fourteen weeks — exactly the period when the puppy is not yet fully vaccinated. The answer is not to keep the puppy locked indoors until sixteen weeks, which creates a fearful adult dog, and it is not to take it to the dog park, which risks parvovirus. The middle path is safe socialisation: carry the puppy in public places, let it meet healthy, vaccinated dogs in clean environments, invite people to the house, and expose it to sounds, surfaces and handling at home. Avoid high-risk places — dog parks, pet stores, pavements where unknown dogs have been — until a week after the final shot. Your vet can advise on the risk in your specific area, because parvovirus and distemper prevalence varies enormously by location.

Common mistakes

The most common mistake is stopping after one or two shots, which leaves the puppy or kitten unprotected. The second is assuming an indoor cat does not need vaccines — panleukopenia and calicivirus can be carried in on shoes and clothing, and rabies is a legal requirement in most places regardless of lifestyle. The third is vaccinating a sick pet — tell your vet if your pet is unwell, because vaccination is usually postponed until it recovers. The fourth is missing boosters: immunity fades, and a dog whose booster is years overdue may need to restart the series. The fifth is giving vaccines bought online or at a feed store — vaccines need cold storage, correct handling and a health check first, and a home-given vaccine may not be valid for licensing or boarding.

When to see a vet

See your vet for the vaccine series, for boosters, and promptly if your pet has a reaction to a vaccine — mild soreness and tiredness for a day are normal, but swelling of the face, vomiting, diarrhoea or collapse need emergency care. Your vet sets the real schedule for your area and your pet's lifestyle, and this page is a general guide, not a prescription. For the deworming schedule that runs alongside vaccination, use the deworming schedule helper; for the puppy's first weeks, the puppy age calculator and the feeding schedule generator.