titre testing & tailored vaccination

Titre testing is not a replacement for vaccination. It determines the moment when vaccination is demonstrably needed again.

A vaccination stimulates the animal to produce antibodies; a titre test measures how many antibodies are in the blood. With a negative result (0 or 1) it is advisable to vaccinate the animal.

Permitted to meet the vaccination requirement

The Netherlands Food and Consumer Product Safety Authority (NVWA) states that titre tests may be used to meet the vaccination requirement. The titre test turns out to have good predictive value for the protection an animal has. The vet must, however, record the result officially in the European passport: the value per disease, the date of testing and the date on which testing must be repeated.

The vaccination requirement applies to keeping dogs and cats commercially, think of boarding, shelters and breeding. For a breeder it applies when more than 20 kittens a year are sold, delivered, taken in or bred. The required vaccinations are then feline panleukopenia (FPV) and cat flu (FCV/FHV): the so-called core vaccines, which protect against serious, globally widespread diseases and which every cat should receive.

Why titre-test?

Some vaccines give far longer protection than the current guidelines prescribe. Several studies (including Scott & Geissinger 1999, Lappin et al. 2002, Schultz 2006) show that immunity from a live attenuated vaccine for feline panleukopenia (FPV) and cat flu (FCV/FHV) lasts at least 3 to 5 years.

On the other hand, it happens that kittens spend their first year of life without protection, because they were vaccinated while maternal antibodies were still present. Every animal receives maternal antibodies through the colostrum in the first 24 hours. These are temporary and disappear gradually, but can remain in the blood for up to 20 weeks, sometimes longer (DiGangi et al. 2012, Jakel et al. 2012). A titre test then offers a solution. In principle a kitten needs to be vaccinated only once: exactly when it is really needed. Do another titre test 3 to 4 weeks after vaccination to see whether the antibodies have been produced.

There is no point at all in vaccinating a kitten or cat that still has (maternal) antibodies in its blood: the vaccine is neutralised by the antibodies already present. The vaccination does not take and the titres are not raised. In such cases it is a matter of unnecessary vaccination.

A kitten is traditionally vaccinated several times (at 9 and 12 weeks). According to the latest guidelines the last kitten vaccination is better given only after 16 weeks, and the booster vaccination has been brought forward to between 6 and 12 months. The hope is that at some point there are no maternal antibodies left, but that really remains a gamble. Vaccinating a few times does not mean a kitten is actually protected. The titre test is therefore ideally suited to measuring, in both young and older cats, whether there is sufficient protection. This avoids unnecessary re-vaccination and lowers the burden on the immune system.

Tailored vaccination

The leading organisations in the field of vaccination, the AAHA (American Animal Hospital Association), the AAFP (American Association of Feline Practitioners) and the VGG (Vaccination Guideline Group) of the WSAVA, all emphasise the value of tailored vaccination. By titre testing, the basic schedule can be individually adapted to an animal's health, age and living conditions. Not vaccinating is no solution, but titre testing is a sensible way to limit vaccination to a necessary minimum and still know that your pet is well protected.

Reliability of the vaccination

The WSAVA/VGG guidelines show that only the FPV vaccine (feline panleukopenia) provides sterile immunity. It prevents the disease. The cat-flu vaccine (FCV/FHV) is also a core vaccine, but offers lower protection. As a result, some cats can still fall ill despite correct vaccination and a positive titre (Pedersen et al. 2000, Schorr-Evans et al. 2003). The chance that the disease runs a milder course is then greater, though.

A close relative of the herpesvirus (FHV) is known in humans as the cause of a 'cold sore': once you are infected, you remain a carrier for life. The same goes for cats. The calicivirus (FCV) changes constantly, just like the human flu virus. Because there are many FCV strains, a cat infected with one strain can still be infected by another. The vaccines therefore use the strains that trigger the broadest possible defence. With FHV this does not apply, as only one strain is known so far. A vaccine that gives 100% protection against cat flu does not yet exist, unfortunately.

A large-scale Chinese field study involving 4,736 vaccinated cats confirms that two primary doses of a trivalent inactivated vaccine already build sufficient protection in most cats, a third dose adds little extra benefit. In addition, approximately 2% of cats showed a suboptimal immune response, possibly due to genetic predisposition (FLA polymorphisms). (Wang et al., Scientific Reports 2025)

Reliability of the titre test

The WSAVA/VGG states that there is an excellent correlation between FPV antibodies and protection. For the cat-flu variants that relationship is more limited. An absent or reduced titre does not, however, always mean that there is no or insufficient immunity: local immunity and cell-mediated (cytotoxic) defence also contribute to protection against viral infections (Lappin et al. 2002).

Moreover, when antibodies are produced, through vaccination or a field virus, memory cells in the lymph nodes are activated that can quickly produce new antibodies as soon as the cat encounters the virus again.

An Italian six-year field study (Dall'Ara et al., Life 2023) examined 740 cats, 435 vaccinated and 305 unvaccinated, to determine how long protective antibody titres (PATs) remain detectable. The results show that vaccinated cats significantly more often and for longer periods display protective titres compared to unvaccinated cats, but that in a proportion of vaccinated cats titres do drop below the protective level over time. This underlines the importance of regular titre testing as a guide for a personalised vaccination schedule.

The Vcheck rapid in-house test for FPV, FHV and FCV has been validated in collaboration with Cornell University (Bionote / Cornell University, n.d.). For FPV a sensitivity of 100% and a specificity of 95.2% were measured against the gold standard (HI test). For FHV these values were 100% and 91.5%, and for FCV 92.7% and 85.3% (against the VN test). The test is therefore reliable enough to serve as a practical screening tool, particularly for FPV.

Side effects of vaccinations

Cats can develop mild signs of illness after a vaccination; an allergic reaction is rare. In places where injections (not only vaccinations) were given earlier, tumours are sometimes described in cats: the so-called injection site sarcoma. The chance of this is small, 0.01 to 0.1%, or roughly 1 to 10 per 10,000 vaccinations. Experts agree that the benefits of vaccinating are many times greater than the drawbacks. But vaccinating must be done at the moment when it makes sense.

The WSAVA's VGG therefore strongly advises vaccinating all dogs and cats against the core diseases wherever possible. Vaccinating protects not only the individual animal but also provides herd protection, which minimises the chance of outbreaks. That herd protection only occurs once 75% of all pets are vaccinated. At the same time the VGG says vaccines should not be given unnecessarily: however small the chance of side effects, it exists. If the animal is still sufficiently protected, the WSAVA advises not to vaccinate, though a regular health check at the vet remains recommended.