It can be scary and confusing when a vaccinated dog comes down with a disease like parvo, which the vaccines are supposed to prevent. As a dog owner, you did the responsible thing by keeping your dog’s shots up-to-date, so how did he still get sick? Understanding a bit more about how vaccines work will help explain why parvo sometimes breaks through.
How Do Vaccines Work?
Vaccines contain either weakened or killed forms of a virus. This allows a dog’s immune system to build antibodies against the virus without your dog having to get sick. That way, if your dog is ever exposed to the real virus, his body is primed and ready to fight it off quickly before it can make your dog sick.
Think of it like doing practice drills before a big game. The drill isn’t the real thing, but it gets you ready for the real thing when it happens.
Why Would a Vaccinated Dog Still Get Parvo?
There are a few reasons why a vaccinated dog might still come down with parvo:
The vaccine didn’t stimulate a strong enough immune response
Just like people, some dogs may not build up sufficient antibodies after getting vaccinated. Maybe their immune system didn’t react strongly enough to the vaccine for some reason. If the antibody levels are low, the dog may not be fully protected.
The parvo strain was different than what’s in the vaccine
Viruses like parvo are always mutating and evolving. Sometimes a new mutant strain pops up that the vaccine isn’t designed to protect against. It’s like getting vaccinated for last year’s flu virus and then getting sick from this year’s different flu virus. Vaccine makers try to stay on top of emerging strains but sometimes a new one slips through.
The dog was exposed to a very high viral load
Vaccines protect from illness, but they don’t form an invisible barrier keeping all viruses out. For any vaccine, there is a threshold level of virus exposure that can overwhelm the vaccine-primed immune system. Think of a vaccinated dog getting exposed to parvo as a game of tug-of-war between the virus and the immune system. If the viral side dumps a huge number of viruses into the fray, it can sometimes overpower the immune system despite vaccination.
There was a window of susceptibility
Vaccines don’t last forever – their protection diminishes over time. At some point, antibody levels drop low enough that a dog is again susceptible to disease. For parvo, usually the protection from a booster vaccine lasts about 3-4 years. Some dogs can be susceptible even earlier if their immune response was particularly weak. This window of susceptibility opens a vaccinated dog up to catching parvo.
The dog was immunocompromised
Dogs who have immune system problems are especially prone to breakthrough infections of vaccine-preventable diseases. Conditions like leukemia, autoimmune disease, or immune-suppressing medications can all diminish a dog’s immune protection from vaccines. Even normal aging weakens the immune system over time. An older vaccinated dog or one with health conditions may have more risk.
What Increases a Dog’s Risk of Breakthrough Parvo Infection?
We’ve covered the main reasons breakthrough parvo infections happen in vaccinated dogs. But what factors specifically increase the risk of parvo breaking through the vaccine’s protection? Here are some of the biggest risk factors:
Young age
Puppies are at the greatest risk, especially before the full vaccination series is complete around 16-20 weeks. Their immature immune systems don’t respond as robustly to vaccines. Maternal antibodies from the mother can also interfere with responding well. Even after the puppy series, protection doesn’t peak until 1-2 weeks after the final shots.
Incomplete vaccinations
Obviously, skipping or delaying vaccine boosters raises the risk of parvo infection. But even just being a little late for a booster can open the window of susceptibility. Sticking tight to the vaccine schedule gives your pup the best protection.
Poor nutrition
Just like in people, diet impacts immune function in dogs. Dogs who are malnourished or eating poor quality diets don’t get the vitamins, minerals, and nutrients needed to maintain robust immunity. Garbage in, garbage immunity out.
Chronic health conditions
Any dog with a compromised immune system is at greater risk of breakthrough parvo infection. Leukemia, autoimmune disease, diabetes, chronic kidney/liver disease, and cancer all diminish the immune system and vaccine efficacy.
High parvo exposure risk
Dogs exposed to lots of other dogs – like those in shelters, daycares, boarding facilities, dog parks, or out on the streets – are obviously at higher risk of encountering parvo. The more viral exposure, the more chance it will break through the vaccine protection.
Overdue vaccines
Once the parvo vaccine booster period has passed (every 3-4 years), the protection is likely worn off. Any dogs not getting re-vaccinated on schedule are sitting ducks for parvo. Set a reminder on your calendar so they don’t miss that booster deadline.
Recent illness or medication
Anything that taxes the immune system – like a separate illness or medications that suppress immunity – can leave a dog vulnerable to parvo for a period of time afterwards. Wait until your dog fully recovers before socializing with other dogs since the vaccine may not be working at full strength.
What Are the Stages and Symptoms of Parvo in Dogs?
Now that you know why vaccinated dogs can still sometimes come down with parvo, let’s look at how the illness typically progresses so you can be alert for signs of infection. Parvo has three main stages:
Incubation (3-10 days)
This is the initial period after exposure while the virus is multiplying inside the dog’s body. At this stage they usually show no symptoms at all. You won’t realize they’re infected quite yet.
Acute illness (2-7 days)
This is when clinical signs start appearing as the virus attacks the intestinal lining, causing severe vomiting/diarrhea:
- Vomiting
- Bloody diarrhea
- Loss of appetite
- Lethargy
- Fever
- Dehydration
This is the most severe and dangerous stage where the dog risks life-threatening dehydration. Hospitalization and intensive treatment are usually needed.
Recovery phase (days to weeks)
If a dog survives the acute illness, the final phase is when the intestine heals and gut function returns to normal. However, full recovery can take weeks. Dogs remain vulnerable to secondary infections in this phase.
How is Parvo Diagnosed?
Because parvo symptoms are common with many intestinal illnesses, diagnostic testing is needed to confirm parvo:
Fecal analysis
This looks for presence of the virus in the feces under the microscope. Results come back in minutes.
ELISA SNAP test
This antibody-detecting blood test provides extremely accurate, rapid results in less than 15 minutes. Just a few drops of blood needed.
PCR test
PCR technology amplifies viral DNA from a stool sample to detect even tiny amounts of virus. Results come back within 1-2 days. Extremely sensitive and specific.
Once parvo is confirmed, treatment focuses on supporting the dog through the acute illness while their immune system fights it off. Intravenous fluids, anti-nausea medication, antibiotics, and other supportive therapies are typical.
What is the Prognosis for Dogs with Parvo?
The prognosis depends on how quickly and aggressively the parvo is treated. With early and intensive veterinary treatment, 70-80% of dogs survive. However, death rates approach 90% once critical dehydration sets in.
Dogs less than 6 months old have the highest mortality rates from parvo, around 20%. Older adult dogs have death rates around 5-8% with treatment. Overall, with veterinary hospitalization the average parvo mortality rate is around 10-15%.
Can a Dog Get Parvo Again After Recovery?
The good news is that dogs build excellent lifelong immunity after recovering from parvo. Re-infection later in life is extremely rare, even if exposed to infected dogs again.
However, it takes 2-4 weeks after recovery for the immune system to produce maximum antibody levels that confer solid protection. So recently recovered dogs remain somewhat vulnerable during that window.
Vaccination After Parvo Recovery
Since parvo recovery generates such strong immunity, some vets advise waiting 3-4 weeks after recovery before giving a routine parvo booster vaccine. This prevents the vaccine antibodies from interfering with the natural antibodies.
Other vets recommend repeat vaccination 3-4 weeks after recovery since the dog’s immune response will be excellent by then. This further boosts antibody levels for added protection.
Discuss the ideal post-recovery vaccination approach with your own vet.
Steps to Prevent Parvo in Dogs
While parvo can sometimes break through, there are many measures all dog owners can take to minimize risk:
Keep puppies current on vaccines
Follow the initial puppy shot schedule very closely, then maintain regular 3-4 year boosters for life.
Avoid unknown dogs
Steer clear of dog parks, daycares, shelters, and public areas where unknown vaccination status dogs frequent. Stick to controlled playgroups.
Clean up poop ASAP
Promptly remove dog poop from your yard to prevent environmental virus buildup. Parvo can persist in soil for years.
Keep unvaccinated puppies home
Don’t take them anywhere public until 2 weeks after their final puppy shots when protection peaks.
Wash hands frequently
Have all family members wash hands after petting unknown dogs to avoid bringing home germs.
Sanitize belongings
If your dogs must go to a higher risk setting like a daycare, sanitize their leash, collar, harness and other belongings afterward.
Know your parvo risks
Be aware of any parvo outbreaks reported in your local area and take extra precautions.
Feed a nourishing diet
Feeding a diet rich in whole foods and nutrients supports good immune function in your dog.
Minimize other illness
Preventing other diseases through routine veterinary care reduces strain on the immune system so vaccines work optimally.
The Takeaway on Parvo in Vaccinated Dogs
While parvo infection in vaccinated dogs is uncommon, it’s important to understand it remains a possibility. This allows you to take smart precautions while also better recognizing signs of illness.
No vaccine offers 100% protection, but following the vet’s vaccine protocol, minimizing exposure risk, and supporting your dog’s overall health are still your best defenses against parvo. Relax in knowing that with proper care, the vast majority of vaccinated dogs live long, healthy, parvo-free lives!