Cats, Vaccinations & Standard of Care 

Paola Dall’Ara

Associate Professor of Veterinary Immunology and Infectious Diseases of Dogs and Cats
Department of Veterinary Medicine and Animal Sciences, University of Milan, Italy

Since antiquity and around the world, cats have become a constant in our lives.

As the years went by, their number has significantly increased. According to the latest demographic analysis*, there are now between 300 to 600 million cats worldwide. They seem to be more common in the United States where there are 75 million (representing the highest feline population in the world), followed by China (53 million), and Russia (almost 18 million). In Europe, there are about 113 million, present mostly in Eastern Europe (Romania, Latvia, Poland, and Hungary), and their number keeps growing.

global cat pet population

Owners’ attention to the care and well-being of these beautiful animals has also increased over time, and today many cat owners regularly visit a vet to check the health status of their furry friends to guarantee their protection against dangerous diseases through vaccination.

Vaccination has always helped to significantly reduce the incidences of many life-threatening diseases both in humans and in pets. It continues to play an important role in preventive medicine today, representing an indispensable mainstay for promoting human and animal health all over the world.

According to the main international pet vaccination guidelines*, pet vaccines are classified as core and non-core. Core vaccines are essential and intended for all dogs and cats since they protect them against dangerous and life-threatening diseases, while non-core vaccines are optional and recommended only for dogs and cats at risk of contracting specific infections. Feline core vaccines protect against Feline Panleukopenia Virus (FPV), Feline Herpesvirus-1 (FHV-1), and Feline Calicivirus (FCV), the last two responsible for the so-called feline Upper Respiratory Tract Infection (URTI). ABCD adds another vaccine category, the “circumstantial” one, in which certain vaccines are required under specific circumstances (eg, cats traveling to areas where rabies is endemic, or cats with outdoor access who are at risk of contracting FeLV).

All cats should receive core vaccines at least once throughout their lifetime for a dual purpose:

to prevent individual infections and to assure herd immunity. In fact, unvaccinated cats represent a risk to the entire cat community by serving as a source of infection for all other cats. Kittens should receive a series of core vaccinations (plus the first two FeLV vaccine administrations) before they are 16 weeks of age as well as their first booster shot (core and FeLV) one year later. 

For decades, subsequent core boosters were traditionally performed on an annual basis.

Nowadays, due to new knowledge and modern vaccines, best practice guidelines for immunization suggest vaccinating adult cats in different ways according to the disease and the cats’ lifestyle: FPV no more frequently than every 3 years possibly using modified live (attenuated) vaccines (MLV), and FHV-1 and FCV depending on each individual cat’s level of risk. In fact, cats are not all the same, and they can be at low- or high-risk. Low-risk cats are generally solitary indoor cats that never visit a boarding cattery or a cat show, while high-risk cats live in a multicat, indoor/outdoor household or regularly travel or visit boarding catteries or feline exhibitions.

The FeLV infection status of all cats should be determined, and only seronegative cats should receive FeLV boosters every 2 years if they are at a low-risk of infection and annually if they are at a high-risk, based on their lifestyle, environment, and overall health status. FeLV vaccination can be discontinued thereafter if there is no further risk.

Cat’s levels of risk are not the only thing that differs. Not all core vaccines are the same either.

In fact, FHV-1 and FCV vaccines can’t always provide the same robust protection as vaccines against FPV (or as canine core vaccines). Consequently, high-risk cats should be vaccinated more frequently than low-risk cats, generally every one or two years depending on the risk of every single cat. Nevertheless, it is possible to see in some cats a long persistence of the specific vaccine-induced protection not only with FPV vaccines but also with respiratory ones (FHV-1 and FCV).

This can occur even if several factors heavily interfere with the amount of adequate immune protection, beginning with the interference of the Maternally Derived Antibodies (MDA) in kittens.

As a result, we now know that the serum antibody concentration specific for feline core vaccines represents a good standard of care. This helps clinicians administer core vaccines appropriately as needed, reducing both vaccination failures and unnecessary vaccinations, and avoiding adverse vaccine events, including the much-feared feline injection site sarcoma (FISS) in cats.

In-clinics tests are rapid and simple serological test kits, based on the ELISA or lateral flow techniques, that can detect and sometimes quantify the presence of protective antibodies exclusively for core vaccines (for other diseases, available rapid tests have only diagnostic value).

While dogs have several commercially available kits, cats have very few testing kits. One of these kits is VacciCheck, which has been registered and validated both for dogs and cats, and in the latter for the determination of serum antibody concentration to FPV, FCV and FHV-1. Different studies report an excellent correlation between the presence of antibodies against FPV and resistance to infection. A positive test result means that the cat is protected, while a negative test result indicates that the cat has little or no protection, and then revaccination is recommended. On the contrary, the correlation between serum antibodies and protection against FCV and FHV-1 infections could be less robust than for FPV, since for these infections mucosal immunity and cell-mediated immunity, respectively, could play an important but not easily measurable role. For this reason, a negative test result for these two respiratory viruses would not necessarily indicate a lack of protection.

In my personal experience, which includes hundreds of cats (as well as dogs that showed a similar pattern), among immunized cats only few had no FCV/FHV antibodies.

Therefore, based on my professional opinion, measuring antibody titers can best reflect the standard of care for both dogs and cats. It is extremely useful in determining the protection of kittens following the first vaccination series, and that of adult cats before they receive booster shots to decide whether revaccination is needed or not.

Rapid antibody titration can also be used in stray cats in determining the prevalence of seropositivity for these three viruses, and in cat shelters to help control FPV outbreaks.

At present, such in-clinics tests might be relatively expensive. However, as pointed out in the last WSAVA guidelines, the principles of Evidence-Based Veterinary Medicine (EBVM) suggest that testing for antibody status is a better, safer, and ultimately more cost-efficient practice than simply administering a vaccine booster haphazardly.

VacciCheck Feline

Recorded webinar

Dr. Paola Dall’Ara