Vaccines are necessary to reduce illnesses in cats caused by infectious diseases. Improvements are continuously being made in vaccine safety and effectiveness.
Veterinarians routinely recommend certain vaccines for all cats (called core vaccines), while others (called non-core vaccines) are used more selectively, according to the cat’s environment and lifestyle. In all cases, decisions about vaccine types and vaccine schedules that are best for each cat require professional advice.
What is a vaccine?
A vaccine is a preparation of killed or altered microorganisms that is administered into the body. The vaccine stimulates the immune system to learn how to fight the microorganism so that if the cat encounters that microorganism in the future, the cat will either not get sick or will have a less severe illness.
How do vaccines work?
Vaccines work by stimulating the body's immune system to recognize and fight a particular microorganism such as a virus, bacteria, or other infectious organism. Once an animal is vaccinated, their immune system is primed or prepared to react to future infection with that microorganism. The vaccine mimics a true infection so the immune system can better protect the body in the future. Depending on the disease, the vaccine will help the body prevent infection or it will lessen the severity of infection and promote rapid recovery.
While a vaccine can prevent illness, it cannot block microorganisms from getting into the body, which means that sometimes a cat may not look sick, thanks to the vaccine, but can still spread the invading microorganisms to other cats. This potential for spread may be important in a breeding colony.
What are the differences between the various types of vaccines?
There are three major types of vaccines.
1. Modified live (live attenuated) vaccines. These vaccines contain live organisms that are weakened so they can still infect cells, replicate, and stimulate an immune response – without causing disease. Modified live vaccines induce a stronger, longer-lasting immunity than inactivated vaccines. Modified live vaccines may not be appropriate for all cats.
2. Killed (inactivated) vaccines. These vaccines are prepared using organisms that have been killed. On their own, they do not give as high a level of protection as the live, replicating type of vaccine, so killed vaccines may have an adjuvant (added ingredient) to make the immune response stronger.
3. Subunit vaccines. These vaccines are more commonly called recombinant vector or DNA vaccines. In these vaccines, the infectious organism has been broken apart, and only certain pieces are included in the vaccine (e.g., surface proteins). These pieces cannot affect the immune system on their own, so they are packaged with something that can do that job called a vector.
Each type of vaccine has advantages and disadvantages. Your veterinarian will consider your cat's individual circumstances when choosing the appropriate type.
How are vaccines administered to cats?
Some vaccines are given locally, for example into the nose, but most must be injected to achieve the maximum stimulation of the immune system. Some vaccines are injected subcutaneously (just under the skin) and others are injected intramuscularly (into the muscle).
Vaccines are often available in combinations that can be given in one dose. Combination vaccines are convenient and avoid extra injections for your cat. Your veterinarian will advise you on the appropriate vaccines for your cat based on their relative risks and lifestyle.
Which vaccines are recommended for cats?
The following core vaccines are currently recommended for all kittens and cats by the Feline Veterinary Medical Association (FelineVMA) and the American Animal Hospital Association (AAHA):
- Feline caliciviruses
- Feline leukemia virus (FeLV) — considered a core vaccine in kittens and one-year-old cats
- Feline panleukopenia virus
- Feline viral rhinotracheitis, also known as herpes virus type 1 (FHV-1)
- Rabies virus
The following non-core (optional) vaccines are recommended by the (FelineVMA/AAHA) for cats with a risk of exposure to specific diseases, include:
- Chlamydophila felis (causes feline chlamydiosis)
- Bordetella bronchiseptica (causes feline bordetellosis)
- Feline leukemia virus (FeLV) in adult cats
Other vaccines may sometimes be appropriate, but are not specifically recommended by the FelineVMA/AAHA, including feline infectious peritonitis (FIP).
What is maternal immunity?
Newborn animals have not had a chance to make their own immunity, so they need protection against infections present in their environment. They receive this immunity from their mother, as maternal antibodies. Most of this passive immunity is transferred to the kitten through the first milk or colostrum. This maternal immunity is only temporary; it declines steadily over the first few weeks of life and is largely gone anywhere between 4 and 16 weeks of age. The rate of decline is variable, depending on many factors.
When should my kitten be vaccinated?
Generally, kittens are vaccinated for the first time between six and eight weeks of age, and booster doses should be given every three to four weeks until 16–20 weeks of age. A kitten will not be fully protected until seven to ten days after completing the vaccination series. Under certain circumstances, your veterinarian may advise an alternative regime.
Why do kittens need more than one dose of some vaccines?
Without complicated testing, it is impossible to know when a kitten loses the passive protection it gets from its mother. An early decline in a kitten’s maternal antibodies can leave it susceptible to infection at a very young age. At the same time, a strong maternal immunity can interfere with early vaccination. Giving a kitten multiple doses ensures that it is protected in either of these situations. In addition, the first vaccine dose is often a “priming” dose, particularly with killed vaccines, and the second dose boosts the response to a higher, longer-lasting level of immunity.
Why does my cat need to be re-vaccinated?
The immunity provided by a vaccine may last a year or more, depending on the type of vaccine and your cat's vaccine history. However, immunity declines with time, and the decline rate varies between individuals. To maintain the best protection against infectious diseases, revaccinations have proven very successful. As vaccines are improved over time, some do not need to be given as often, depending on individual circumstances. Your veterinarian will discuss the need and frequency of booster vaccinations for your dog based on your cat’s needs and lifestyle.
How long does it take a vaccine to produce immunity?
Within a few hours of vaccination, the earliest phases of the immune response are stimulated. It is usually 10 to 14 days before a reasonable level of protection is established. Killed vaccines may not provide adequate protection until after the second dose. In young kittens, maternal antibodies may hinder protection until later in the vaccine series. Therefore, it is advisable wait until a kitten has finished its full vaccination course before allowing close access to other cats and kittens of unknown vaccination history.
What happens if my cat is sick when vaccinated?
In most cases, minor illnesses do not have disastrous consequences, but it is important that an animal is healthy when vaccinated to ensure the proper development of immunity. To ensure your cat is healthy before vaccination, your veterinarian will perform a check-up before vaccination and will sometimes do pre-vaccination blood tests.
What are the risks of vaccination?
There are very few risks associated with vaccination. Your veterinarian can advise you on specific details concerning your cat. You may notice your cat has a temporary loss of appetite or is less lively a day or two after a vaccination, but this should resolve within 24–48 hours. Very few cats may be allergic to one or more components of the vaccine and have more serious side effects, such as vomiting, diarrhea, or difficulty breathing. If these signs occur, contact your veterinarian immediately.
In a very small number of genetically susceptible cats, a rare form of soft tissue sarcoma has been associated with a reaction to vaccine components or any injectable substance (known as vaccine-associated or injection-site fibrosarcoma). The benefits of vaccination greatly outweigh these small risks in most situations.
Do vaccines provide 100% protection?
Vaccines have been highly successful in protecting most cats against disease. As a direct result of vaccination, previously common diseases are now rare. However, there are situations in which the cat’s immunity may be overcome, and a vaccinated cat may still develop disease. In such cases, the disease is generally milder than it would have been had the cat not been vaccinated. Some causes of apparent vaccine failure include the following:
New or varied virus strains. Some viruses have different strains or evolve into new strains that are not directly covered by the vaccines given. In these cases, the vaccine may give some cross-protection or partial protection, but protection may not be complete. This is particularly a problem with feline calicivirus infections, which has many different strains, like the common cold in people.
Maternally derived antibodies. Kittens acquire maternal antibodies from the mother (through the uterus before birth and from the milk during nursing). A well-vaccinated mother cat passes antibodies to her kitten, and these antibodies protect the vulnerable kitten against those diseases for the first two to three months of life. However, during this same period, the antibodies from the mother can block the kitten’s ability to respond to vaccination.
This blocking effect decreases over time as the maternal antibodies gradually disappear, to a point when vaccination can be successfully given. This time range varies between kittens, so booster vaccines are recommended frequently, until the kitten is older.
Incomplete immune response. Cats’ immune systems vary. A cat’s immune system may underperform due to disease, sickness, stress, or complications associated with advanced age. Some cats respond less well to vaccination, so immunity may be incomplete or shorter-lived than normal. Certain breeds and genetic lines have a tendency for such problems.
Declining immunity. Immunity to a specific organism declines over time, without booster vaccinations or the natural boosting of immunity by sporadic exposure to the infectious agent in nature. This decline is particularly evident in older dogs. Eventually, immunity will be too low to prevent disease.
Immune suppression. Certain infections and some drugs, such as anti-cancer drugs, may suppress the immune system so that an otherwise well-vaccinated cat becomes susceptible to infection and disease.
It is important to remember that not all vaccines can completely prevent illness; some vaccines are designed to decrease the severity of disease, but the disease is still possible. If you feel your dog has contracted an infection for which it has been vaccinated, let your veterinarian know. Tests can be done to establish why vaccination has failed to be protective.
