Once your dog's puppy vaccination course is done, the job shifts from a fixed schedule to an ongoing decision: which annual booster is right for them? Walk into any vet clinic and you'll hear vaccines referred to as C3, C5 or C7, and it's not always obvious what the difference actually is or which one suits your dog.
This guide breaks down what each option typically covers and the factors that go into choosing between them. It's general information, not a recommendation for your dog specifically - your vet is the only one who can weigh up their age, health, lifestyle and local disease risk, so treat this as a starting point for that conversation, not a substitute for it.
What do C3, C5 and C7 actually cover?
Naming conventions vary between vet clinics and vaccine brands, and this isn't an exhaustive list. Some clinics also use terms like C4 (often a step between C3 and C5, such as C3 plus a kennel cough component) or C6, and even C7 formulations differ - some add leptospirosis alone, others add leptospirosis and coronavirus together. Broadly, though, the most common annual options are:
| Vaccine | Typically covers | Often suited to |
|---|---|---|
| C3 | Parvovirus, distemper and canine hepatitis (the three core diseases) | Dogs with low exposure to other dogs and public spaces |
| C5 | Everything in C3, plus parainfluenza and Bordetella bronchiseptica (canine cough) | Dogs attending daycare, boarding, training classes or dog parks |
| C7 | Everything in C5, plus broader protection that typically includes leptospirosis, and depending on the brand or clinic, sometimes coronavirus | Dogs in higher-risk areas for leptospirosis, or where a vet recommends the broadest coverage |
Some clinics also offer leptospirosis or coronavirus components separately depending on regional risk. Because formulations vary by brand and clinic, always confirm exactly what's included in the vaccine your vet is recommending before your dog's appointment.
The diseases behind the letters
Canine parvovirus is most serious in young pups and older dogs. It attacks the intestines, causing bloodstained diarrhoea, vomiting and severe abdominal pain, and dogs can die from dehydration despite intensive veterinary care. Direct contact with an infected dog isn't even necessary - the virus is persistent enough that an infected dog's environment needs disinfecting to stop it spreading, and outbreaks occur regularly across Australia, especially over summer.
Canine distemper is highly contagious, with young puppies at highest risk. Symptoms range from fever, coughing and nasal discharge to vomiting and diarrhoea, progressing to muscle tremors, fits and paralysis later in the disease. Treatment is often ineffective, and dogs that recover can be left with permanent brain damage.
Canine hepatitis is another highly contagious and often fatal viral disease. Severe cases are rare in dogs over two years old, but in younger or unprotected dogs it can bring on high fever, vomiting and acute abdominal pain, with death possible within 24 to 36 hours. Dogs that recover can develop long-term liver and kidney problems and may shed the virus for months.
Canine cough (often called kennel cough) isn't one disease but a cluster of infectious agents, including the bacterium Bordetella bronchiseptica and the parainfluenza and adenovirus type 2 viruses, that spread wherever dogs mix, such as parks, shows, obedience schools and boarding kennels. It produces a dry, hacking cough that can drag on for weeks, and while mostly just distressing for pet dogs, it's a bigger problem for working and sporting dogs and can occasionally progress to pneumonia.
Canine coronavirus causes depression, appetite loss, vomiting and diarrhoea, especially in younger dogs. Most dogs recover with treatment, but it can be fatal, particularly if a dog is also fighting parvovirus at the same time.
Canine leptospirosis is spread by the urine of rats, usually picked up through contaminated food and water or rat bites. Risk climbs where rat populations are high, such as rubbish dumps or cane-cutting areas, and after long wet periods that force rats to move or concentrate. It's also zoonotic, meaning it can pass to humans, who may then suffer a persistent flu-like illness.
Factors that may influence the right choice for your dog
- Lifestyle - a dog that regularly visits dog parks, boarding kennels, grooming salons or training classes is exposed to more dogs, and more risk, than one that mostly stays home and in the backyard
- Location - leptospirosis risk varies significantly by area, particularly near waterways, high rat populations, or after extended wet weather
- Age and health status - older dogs, dogs with existing health conditions, or those on certain medications may need a tailored approach
- Local disease activity - outbreaks of parvovirus or other diseases in your area can shift what your vet recommends in a given year
Caring for your dog after their booster
It's common for dogs to be a little off-colour for a day or two after vaccination, or to have some slight swelling or tenderness at the injection site. Access to food and water and a comfortable area to rest is usually all that's required for a quick recovery. If the response seems more severe than that, contact your vet for advice.
Talk to your vet
This article is intended as general background reading, not veterinary advice, and isn't a substitute for a proper consultation. Your vet knows your dog's history and can assess their individual risk factors to recommend the right vaccination protocol, whether that's a C3, C5, C7 or something else entirely. If your dog is due for a booster, book a chat with their veterinarian to work out what's genuinely right for them.
