Know Your Dog's Risks When Mixing Vaccines and Flea Treatments

Although flea treatments and vaccinations can be beneficial, when they're put together, they are a potentially dangerous mix.

Updated July 8, 2023
Dog at their vet getting a checkup.

Vaccinations and flea treatments are both measures we take to protect our dogs. Little do we know, putting them together could be dangerous for our dog's health. If you haven't heard about the dangers of combining vaccinations and flea treatments, understanding this could save your dog's life.

Dangers of Combining Vaccinations and Flea Treatments

When a dog is vaccinated, it introduces antigens into their body, triggering the immune system to produce antibodies to fight the specific disease. This process essentially trains the immune system to identify and combat this disease if your dog is ever exposed to it in the future.

Since both vaccinations and flea treatments put added strain on your dog's body, administering them simultaneously or too close together could potentially overtax your pet's immune system. This is especially true for puppies, older dogs, and those with existing health conditions, whose immune systems might already be under strain.

Pet expert Wendy Nan Rees has first-had experience of a negative outcome in a vet's office. Her friend had boarded her dog at a vet's office while she was away on an extended trip, and her friend's dog passed away during her vacation.

"They gave the dog all of her regular vaccinations, after which they gave her a special flea and tick vaccine, and then they bathed her," Nan Rees said. "It was just too much for her system to handle. She went into what is called IMHA, or Immune Mediated Hemolytic Anemia."

Fast Fact

Dogs who receive multiple vaccines all at once are twice as likely to experience a negative side effect.


Immune Mediated Hemolytic Anemia (IMHA) is a red blood cell disease with a double whammy, Nan Rees stated. While vaccines are beneficial to boost immunity to certain viruses, the process of vaccination is very traumatic to the body.

"First of all, the body is not regenerating any new red blood cells at the bone marrow level, so eventually the body becomes anemic as the glands and organs become oxygen starved," Nan Rees said. "Second, the body's immune system has gone bonkers. It thinks the remaining healthy red blood cells are bad and starts to destroy them as foreign invaders."

Immediately after the vaccination, the body's immune system will be depressed while the body naturally starts to recover from the shock of the vaccination process. If the vet gives too many vaccines at once or administers a vaccine to a body whose immune system is already compromised, the dog could have problems.


Vaccinosis is a term used to describe any adverse effects from vaccinations. This can include everything from allergies to fever, cancer, or anything else that results from a compromised immune system after vaccination. For instance, if your dog has a chronic disease or for any reason is not completely healthy, it should not be vaccinated. If they are, the dog could develop more serious problems.

All vaccines carry a label that states "For use in healthy animals only." Many jurisdictions will accept an exemption letter from your veterinarian attesting to the fact that your pet is at high risk for vaccination complications if they are sick or being treated for a disease and so they cannot be vaccinated.

Tips for Safe Vaccinations

Keeping your dog safe means staying vigilant. According to pet expert Wendy Nan Rees, these are the general rules you should follow:

  • Always request a blood titer first to check your dogs' current immunity levels. Your dog may not need an immunization.
  • Do not allow more than one vaccine at a time, and no two vaccinations within a three- to four-week period.
  • Never vaccinate your pets if they are sick or currently receiving veterinary treatment.
  • If your pet has a chronic health condition, consult your holistic vet to see which additional risks might be involved in vaccinating your pet.
Quick Tip

Investigate alternatives, such as titer testing and getting an exemption letter from your vet to show your local authorities why you are not vaccinating your dog at that time.

Be Your Dog's Guardian

If you take nothing else away from this tip, please do take this: it is up to you and no one else to be your dog's guardian. You need to do what you believe is correct no matter what. It's alright to tell your vet that you don't want your dog to have his boosters and flea treatment all at once, and there's nothing wrong with requesting a blood titer to check whether your dog needs a booster at all. A little extra caution just might prevent a tragedy.

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Know Your Dog's Risks When Mixing Vaccines and Flea Treatments