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Side effects of vaccines for cats

Following the vaccination schedule in cats saves many lives every year, both in the feline species and in many others, and keeps under control serious diseases, especially in cats that go abroad or that are in colonies or communities. That is why they have a vital importance.

However, as with most drugs, they may present a series of Adverse effects or unexpected reactions that it is convenient to know, without forgetting that the beneficial effects are much greater than the possible damages in the majority of cases. To minimize possible adverse effects, we will always comply with the vaccination schedule according to the age and environment of our cat, according to the indications from our veterinarian and, of course, always complying with the appropriate safety measures, so that they can only be administered by a qualified professional, after the animal has been examined in order to detect any possible sign of illness that might discourage vaccination.

In this article we will detail you the side effects of vaccines for cats, so that you have the most information at your fingertips at the time of vaccinating your feline companion. We have classified the vaccine reactions according to their severity in 2 large groups:

1. Mild reactions

Its the most frequent and they are characterized by having a favorable prognosis. That is, they are those that usually disappear by themselves and they do not usually require any kind of treatment. They usually appear a few hours or a few days after vaccination and usually last from a few days to several weeks. They are related to the activation of the immune response and inflammatory processes.

The main mild reactions are those described below:

Inflammation at the point of inoculation

It is usually a small painful nodule in the area where the vaccine has been administered and usually disappears spontaneously between 2 and 5 weeks post-vaccination. They are usually associated with the adjuvants, proteins or stabilizers that the vaccines contain. We can relieve the area and help the inflammation disappear more quickly applying moist heat in it and doing massages.

It has no clinical importance than the slight discomfort it causes in the animal, except in cases where it is complicated necrosis, fibrosis and / or the appearance of an abscess. In these cases we must go to the veterinarian to treat these complications. Furthermore, if we observe that the nodule does not decrease after the expected time, or even that it increases in size or changes its appearance, it is advisable to perform a puncture to rule out granulomas (due to chronic inflammation), abscesses (secondary infection) or even the appearance of a malignant tumor called fibrosarcoma, which we will discuss in more detail at the end of the article.


Fever in cats appears, as we have mentioned previously, because of the activation of the immune response and, unless it compromises the quality of life of the cat, it is not necessary to treat it. On the day of the vaccine and a couple of days later, it is advisable not to exercise much to the patient or overwhelm, providing a comfortable and quiet place where you can rest and recover without problems.

Lethargy and anorexia

It is usually a consequence of fever and it usually disappears when it disappears. Once again, we will let the cat rest and we will not force him to eat if he does not want to. We can offer it moist and tempered food so that you find it more appetizing and consult with our veterinarian if you are very apathetic or do not want to eat anything for more than 24 hours.

Vomiting and / or diarrhea

It is another of the systemic signs related to the response of the animal’s immune system and the associated inflammatory process. In general, it is about mild processes, but as we will see later, it can occur acutely prior to a more serious reaction, so in case of observing these digestive symptoms, the most advisable is for the veterinarian to explore the animal to assess its status and treat it if necessary.

Regional lymphadenopathy

It is part of the normal response of the immune system and as the days go by, the size of the lymph nodes should return to their normal size.


They can occur in the case of vaccines that are inoculated intranasally (vaccine against PIF) and usually last a few minutes or at most several hours after the administration of the same. They can be accompanied by sniffing and rubbing the snout against surfaces.

2. Serious reactions

In this case they are very rare and they usually have a forecast of reserved to serious. They can appear from the minutes following the vaccination to the following weeks. The main serious reactions are the following:

Hypersensitivity reaction

These are exaggerated reactions of the immune system against substances that would normally be considered harmless under normal conditions. The most common hypersensitivity reaction after vaccination is that of type I or allergic, whose effects are immediate (between 30 minutes and 2-3 hours after administration of the vaccine). The immune system can trigger this reaction to any component of the vaccine.

The symptoms associated with this type of hypersensitivity are caused by a high release of histamine, which is an inflammatory mediator, which increases vascular permeability and causes contraction in the smooth muscle. When this type of reaction occurs, we can observe from generalized pruritus, with the appearance of wheals or redness of the skin (erythema and urticaria) to inflammation of the face and neck due to the appearance of a facial and periorbital edema known as angiedema, and / or respiratory signs due to inflammation of the respiratory tract (which can become obstructed), arriving in the worst case yet anaphylactic shock, which can lead to respiratory failure and fulminating vascular collapse.

In the cat, moreover, it can be seen prior to anaphylaxis, acute vomiting and diarrhea, sometimes hemorrhagic, followed by extreme lethargy, hypovolemia and respiratory and vascular failure, which can be fatal. If we observe any of these symptoms, we should go urgently to our veterinarian to start treatment as soon as possible.

Fibrosarcoma at the point of inoculation

This tumor It has been related to some components of vaccines and other injectable drugs, and usually appears after months or even years of vaccination, being more likely the older the animal is. Although it is very rare and does not tend to metastasize, it is a very aggressive malignant tumor locally, which requires an extirpation with wide surgical margins and has a high tendency to recur, so that in the long term it usually has a poor prognosis.

Since it usually appears at the point of inoculation, it is recommended rotate that point and prioritize areas such as extremities or tail, which allows amputation if necessary and reduces the risk of recurrence. There are cases in which the Surgical treatment with the chemotherapy, according to its evolution and according to how advanced or extended it is.

This article is merely informative, in .com we do not have the faculty to prescribe veterinary treatments or make any kind of diagnosis. We invite you to take your pet to the veterinarian in case of any type of condition or discomfort.

If you want to read more articles similar to Side effects of vaccines for cats, we recommend you to enter in our Vaccination section.

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