Core Vaccines — What Each One Does

DA2PP — The "Core Combo" (Distemper, Adenovirus, Parvovirus, Parainfluenza)

This combination vaccine is sometimes called the "5-way" or "DHPP" vaccine. It protects against four separate diseases in a single shot. It's the most important vaccine your dog will ever receive.

• Canine Distemper

  • Distemper is caused by a virus closely related to measles. It attacks the respiratory, gastrointestinal, and neurological systems simultaneously — and there is no cure. Once a dog develops neurological signs, the disease is almost always fatal or leads to permanent brain damage.

  • Signs: Starts with fever, runny nose, and eye discharge — then progresses to vomiting, diarrhea, seizures, and muscle twitching. Neurological symptoms (seizures, loss of coordination, "chewing gum" jaw movements) can develop weeks or months after the initial illness.

  • Mortality rate: Up to 50% in adult dogs, up to 80% in puppies.

  • How it spreads: Airborne exposure from infected dogs or wildlife (raccoons, foxes, skunks are common carriers).

  • Vaccine protection: Highly effective. The disease essentially disappeared from the vaccinated dog population and only resurfaces in unvaccinated communities.

• Canine Parvovirus

  • Parvo is one of the most feared diseases in dogs — and for good reason. It attacks the rapidly dividing cells of the intestinal lining and the bone marrow, destroying the gut's ability to absorb nutrients and gutting the immune system at the same time. Puppies between 6 weeks and 6 months are the most vulnerable.

  • Signs: Severe, often bloody diarrhea; uncontrollable vomiting; extreme lethargy; loss of appetite; fever. Dehydration sets in rapidly. Dogs can go from sick to critical in 24–48 hours.

  • Survival rate without treatment: Less than 10%. With aggressive hospitalization (IV fluids, supportive care): 70–90%.

  • How it spreads: Through contact with infected feces. The virus is extraordinarily hardy — it survives on surfaces, in soil, and in the environment for months to years, and is resistant to most household disinfectants. An infected dog doesn't even need to be present — their paw prints on a sidewalk can transmit the virus.

  • Vaccine protection: Highly effective. Do not take unvaccinated puppies to dog parks, pet stores, or areas where unknown dogs have been.

• Adenovirus (Infectious Canine Hepatitis)

  • Caused by Canine Adenovirus Type 1, this disease attacks the liver and can cause acute liver failure in severe cases. The Type 2 adenovirus (which the vaccine actually contains) provides cross-protection against Type 1 while also contributing to kennel cough protection.

  • Signs: Fever, lethargy, vomiting, abdominal pain, jaundice (yellowing of eyes/skin), sometimes a characteristic "blue eye" (corneal cloudiness).

  • Vaccine protection: Highly effective; included in the standard DA2PP combination.

• Parainfluenza

  • A virus that contributes to kennel cough. Usually causes mild upper respiratory illness on its own, but combines with other pathogens to produce more serious infections.

  • Signs: Cough, runny nose, mild lethargy.

  • Vaccine protection: Included in the DA2PP combo. Also available as a standalone intranasal vaccine alongside Bordetella.

Rabies

• Rabies vaccination is required by law in all 50 U.S. states — and for good reason. Rabies is 100% fatal in unvaccinated animals and humans once symptoms appear. There is no treatment. It is transmitted through the bite of an infected animal.

• Signs in dogs: Behavior change is often the first sign — a friendly dog becoming aggressive, or a normally active dog becoming withdrawn. This is followed by hypersalivation (the "foaming at the mouth" symptom), paralysis, and death. By the time symptoms appear, the outcome is inevitable.

• Wildlife reservoir: Bats, raccoons, foxes, and skunks are the primary carriers in the U.S. Any contact between your dog and wildlife is a potential exposure.

• Schedule: First dose at 14–16 weeks of age. Booster at 1 year. Then either annually or every 3 years depending on your state's laws and the specific vaccine used. Your vet will know your state's requirements.

• If your dog is bitten by a potentially rabid animal: Contact your vet and local animal control immediately. Even vaccinated dogs may need a booster and observation period per state protocol.

Leptospirosis

• As of 2022, AAHA recommends leptospirosis vaccination for most dogs — it is effectively a core vaccine for the majority of pets.

• Leptospirosis is a bacterial infection spread through the urine of infected wildlife — primarily raccoons, skunks, opossums, squirrels, and rats. The bacteria survive in standing water, puddles, soil, and mud. Urban and suburban dogs are at just as much risk as rural dogs — rats are everywhere, and puddles are everywhere.

• High-risk situations include drinking from puddles or natural water sources, roaming in rural or wooded areas, exposure to wildlife, living in flood-prone areas, or visiting dog parks.Leptospirosis can infect humans. It's one of the most common zoonotic diseases in the world.

  Signs: Fever, lethargy, loss of appetite, vomiting, muscle pain, and in severe cases, acute kidney or liver failure, bleeding disorders, and death.

• Schedule: Two initial doses 2–4 weeks apart, then annual boosters.