Vaccines for dogs and cats are safe, especially compared with the risk of disease. Most animals don’t have any untoward symptoms after receiving a vaccine. But vaccines, like any other medicine, can have some side effects.

Vaccination produces an immune response, and inflammation is part of the immune response. Most of the symptoms (if any) that animals have after vaccination are caused by normal inflammation, meaning that the immune system is acting the way it’s supposed to act when it’s stimulated.

Allergic (hypersensitivity) reactions to vaccines are uncommon in dogs and cats but can be serious. These reactions are caused by an inappropriate immune response. The most severe type of hypersensitivity reaction is anaphylaxis, which can be life threatening.

In one study of dogs in the United States, the rate of vaccine-associated adverse events, including everything from normal inflammatory responses to anaphylaxis, was 0.38% (38 events per 10,000 vaccine doses). Anaphylaxis accounted for 1.7% of the adverse events. The risk of adverse events was highest in small-breed dogs and dogs who received multiple vaccines at the same time.[1]

Mild Symptoms
These are some of the common mild vaccine effects you might notice in your dog or cat. In most cases it’s safe to monitor these symptoms at home. If any of these symptoms last longer than a day or if your pet seems very uncomfortable, contact your veterinarian.

• Mild pain where the vaccine was injected
• Decreased activity or seeming tired
• Loss of appetite
• Sneezing after a vaccine given in the nose

More Serious Symptoms
Allergic reactions to vaccines appear minutes or several hours after vaccination. Anaphylaxis can start with these symptoms and is a medical emergency. Seek veterinary care right away if your pet has any of these symptoms.

• Swelling of the face
• Hives (welts or bumps under the skin, usually itchy)
• Vomiting or diarrhea
• Coughing or difficulty breathing
• Collapse

Lumps at Injection Sites
Most small, firm lumps at vaccine injection sites are caused by inflammation and resolve in a couple of weeks without treatment. An injection-site lump or swelling that is still present after 3 weeks or is enlarging should be checked by a veterinarian. Injection-site cancer is rare but can happen in cats (vaccine protocols and formulations for cats minimize this risk as much as possible).

Autoimmune Disease?
Vaccines could—at least in theory—be linked to autoimmune diseases, in which the immune system targets cells of the body. Immune-mediated hemolytic anemia (affecting red blood cells) and thrombocytopenia (affecting platelets) occur in animals, but the association of these disorders with vaccination isn’t clear.[2] The presence of an autoimmune disease would affect future vaccination decisions for the animal, though.

If Your Pet Has Had a Vaccine Reaction
Tell your veterinarian if your pet has had any vaccine-related symptoms. Your veterinarian will determine if your pet most likely had a normal inflammatory response or an allergic reaction. The decision on how to proceed with future vaccinations depends on the symptoms, the animal’s overall health, and the animal’s individual risk for vaccine-preventable diseases.

Depending on the circumstances, options for future vaccinations might include dividing vaccines among several visits instead of giving multiple vaccines all at once, giving medication (like an antihistamine) before vaccination, using a different type of vaccine, or discontinuing a vaccination. Vaccine titers—levels of antibody in the blood—indicate whether an animal is likely to still be protected by earlier vaccines, so titer testing can replace vaccination in some cases.[3]

Some of these options don’t apply to rabies vaccination, which is mandated by law. In North Carolina and South Carolina, as in many states, veterinarians cannot give medical exemptions for rabies vaccination, and rabies antibody titers can’t be used instead of vaccination.[4]

References
1. Moore GE, Guptill LF, Ward MP, et al. Adverse events diagnosed within three days of vaccine administration in dogs. J Am Vet Med Assoc. 2005;227(7):1102-1108. doi:10.2460/javma.2005.227.1102
2. Tizard IR. Adverse consequences of vaccination. Vaccines for Veterinarians. 2021;115-130.e1. doi:10.1016/B978-0-323-68299-2.00019-8
3. AAHA canine vaccination guidelines: vaccine adverse reactions. American Animal Hospital Association. Accessed August 27, 2021. https://www.aaha.org/aaha-guidelines/vaccination-canine-configuration/frequently-asked-questions/how-can-adverse-reactions-be-managed/
4. Rabiesaware.org. Accessed August 27, 2021. http://www.rabiesaware.org/

Photo by Raghavendra V. Konkathi on Unsplash

Most skin lumps in dogs are benign. In cats, skin masses are more likely to be malignant. It’s impossible to know if a mass is benign or malignant just by looking at it and feeling it. For diagnosis, a sample of cells from the mass must be examined under a microscope.
 
Veterinarians use either fine-needle aspiration or biopsy to take samples from skin masses. Fine-needle aspiration is a quick technique that doesn’t require anesthesia. The veterinarian uses a syringe and needle (about the same size used for dog and cat vaccines) to remove a small sample from the mass. The sample is transferred to a microscope slide and either checked at the veterinary clinic or sent to a laboratory for a pathologist to evaluate.
 
Biopsy is the removal of a section of a mass—or an entire mass, if it’s small—for submission to a laboratory. Biopsy requires at least local anesthesia; most patients need sedation or general anesthesia. Fine-needle aspiration doesn’t always yield enough cells for a definite diagnosis, so biopsy is necessary for some masses.
 
So when is it okay to just watch a lump to see if it gets bigger, and when should a lump be checked by a veterinarian? Masses that fit these criteria should be evaluated by aspiration or biopsy:[1]

• Size of a pea or larger (1 cm or more in diameter)
• Present for 1 month or longer
• Enlarging rapidly or changing in appearance

 
The advantage of evaluating masses while they’re small is that malignant skin tumors can often be cured if they’re removed early. Larger masses are harder to remove completely. Some types of skin cancer spread through the body (metastasize) over time.
 
Benign Masses
Benign masses don’t metastasize to other areas of the body or damage the tissues around the mass. Once diagnosed, they can be left alone unless they become painful or annoying to the animal (for example, if the surface becomes irritated or the mass grows large enough to interfere with movement). These are some of the most common benign skin lumps in dogs and cats:[2,3]

• Lipomas: These masses made of fat lie just under the skin. Some malignant tumors feel just like a lipoma, so never assume that a new soft lump under the skin is a lipoma even if the animal already has several lipomas.
• Papillomas (warts): These small, firm tumors on the skin surface are sometimes nicked by clippers during grooming.
• Cysts: Cysts are fluid-filled masses. Draining the fluid with a needle and syringe will shrink the cyst, but in time the cyst will usually refill with fluid.
• Histiocytomas: These raised, hairless masses are most common in young dogs. Histiocytomas eventually shrink and disappear on their own.
• Melanomas: In dogs and cats, melanomas located on the skin are usually (not always) benign. Melanomas in other areas of the body, like the mouth and the eye, are typically malignant.

 
Malignant Masses
Malignant masses are cancerous and invade the surrounding tissues or metastasize throughout the body. Some malignant skin tumors that can’t be cured with surgery can be treated with radiation or chemotherapy. Animals with skin cancer benefit from referral to a veterinary oncologist. These are some of the malignant skin tumors that affect dogs and cats:[2,3]

• Mast cell tumors: Mast cell tumors vary in appearance and can mimic lipomas. All mast cell tumors should be surgically removed and graded by a pathologist. Surgical removal is sufficient for low-grade mast cell tumors. High-grade mast cell tumors tend to metastasize and need additional treatment.
• Squamous cell carcinoma: This type of cancer may look like an ulcerated or bleeding area on the skin. Squamous cell carcinoma is associated with sun exposure in animals, just as it is in humans.
• Skin gland tumors: Although some tumors arising from skin glands are benign, others (like apocrine gland adenocarcinoma) are malignant.
• Fibrosarcomas: These cancers are locally aggressive (they invade surrounding tissue). In cats, fibrosarcomas occur at injection sites of certain vaccines and other substances. Injection-site tumors are uncommon, but feline vaccination guidelines take into account the small risk of fibrosarcoma, and vaccines that minimize the risk of fibrosarcoma are available.

 
References
1. Ettinger S. See something, do something. Why wait? Aspirate. In: Proceedings of the NAVC Conference, Volume 30: Small Animal and Exotics. NAVC; 2016:720-722.
2. Gear R. Lumps and bumps: common skin tumors. British Small Animal Veterinary Congress 2008. Veterinary Information Network. Accessed August 3, 2021. https://www.vin.com/apputil/content/defaultadv1.aspx?id=3862939&pid=11254&
3. Five types of skin cancer in dogs. NCSU College of Veterinary Medicine. Accessed August 3, 2021. https://cvm.ncsu.edu/wp-content/uploads/2018/03/5-Types-of-Tumors.pdf
 
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