Kitten vaccinations and immunity

Ensuring kittens have an optimal vaccination schedule whilst creating positive patient experiences at the veterinary clinic can be a win-win situation, as Kelly St. Denis describes.

Introduction

Feline Vaccinology has experienced dramatic shifts over the last few decades. While the infectious agents against which we vaccinate kittens have not changed greatly, in other contexts there has been immense change. There has been progress in our knowledge and understanding of some of these infectious agents and the role of vaccination in their prevention; there have been many changes in recommendations for timing, age and frequency of vaccinations and booster vaccinations; we have additional knowledge about maternally derived immunity and its impact on immunity; the scientific design of available feline vaccinations has changed dramatically; and the approved and recommended sites of injection have been modified. Furthermore, the way we interact with our feline patients has been revolutionized by the adaptation of Cat Friendly principles. These changes make vaccinology in the feline species more challenging to implement but more rewarding than ever before. They also impact all life stages of the domestic cat, with the foundations for immunity and Cat Friendly visits being laid in the first year of life. This article will review vaccination protocols and their implementation for the juvenile pet cat primarily from a North American viewpoint, and the reader is encouraged to seek further detail for all life stages in the recently updated AAHA/AAFP guidelines * [1].

* AAHA: American Animal Hospital Association; AAFP: American Association of Feline Practitioners

Maternal-derived immunity

Maternal immunity, in the form of maternally derived antibodies (MDA), is passively transferred from the immune queen to kitten during lactation. Transplacental transfer of antibodies is not significant in the feline species [2]. The availability of immunoglobulins IgA and IgG to the neonate is impacted by the concentration of the proteins in colostrum, the volume ingested, and the capacity of the neonatal intestine to absorb the protein, all of which are largely time-dependent. The immunoglobulin concentration is highest in the colostrum, with levels rapidly decreasing 3 days post-partum [3]. The neonate absorbs the immunoglobulins primarily in the first 24 hours of life, although evidence suggests that absorption decreases dramatically after only 16 hours [3]. Kittens that do not ingest sufficient colostrum during the first 24 hours post-partum will be at risk of failure of passive transfer, increasing the potential for infectious disease during a period when the immune system is undeveloped.

MDA persist in the kitten for variable time periods, dependent on the antibody titer of the queen and the amount of immunoglobulin absorbed by the neonate. A nadir may be reached as early as 3 to 4 weeks of age [2], although some kittens maintain high levels beyond 16 weeks [4]. While MDA provides protection in the immune incompetent neonate, it is described as one of the most common reasons for vaccine failure [1]. Through a negative feedback mechanism, serum MDA can interfere with neonatal production of immunoglobulins, and its presence can also lead to neutralization of vaccine-delivered antigens, thus limiting the vaccine response. There is therefore a “window of susceptibility” between loss of MDA and development of individual immunity, when the MDA levels may be high enough to interfere with the development of vaccine-dependent immunity but insufficient to protect against natural infection [1]. This window of susceptibility must be considered when developing vaccination protocols for kittens. For this reason, vaccinations against feline viral rhinotracheitis/calicivirus/panleukopenia (FVRCP) have increased likelihood of success if given every 2-4 weeks until a kitten is at least 16-20 weeks of age [1]. The exact interval between booster vaccinations should follow manufacturer guidelines, but a final booster is ideally administered 3 to 4 weeks after MDA has decreased below interference levels, which can vary between litters, between kittens within litters, and with the infectious disease being vaccinated against. Recent guidelines [1],[5] recommend replacing the 1-year FVRCP booster with a 6-month booster against FVRCP.  [...]