parasuisremained above the positive level until three weeks of age [54]. reduced production parameters and increased animal collapses, resulting in economic losses. It is well known that pathogens are responsible for most of the economic losses in the livestock sector [2,3]. These days, one of the most important approaches to controlling infectious diseases is vaccination. Considering the increasing trends of restricted antibiotic use to inhibit antimicrobial resistance, proper vaccination protocols may become even more important; vaccines are among the five most effective alternatives to antibiotics [4]. Numerous vaccines were proven to be efficient in protecting pigs against infections with various pathogens, bacterial as well as viral, or against infections adverse effects. Nevertheless, in some cases, vaccines can be less effective than expected or even completely CR1 inefficient. Even using the same vaccine, immunisation efficacy can differ among particular individuals [1,3]. It may result from an abundance of factors that can influence vaccination [5]. Approximately 40 factors that can impact this process were determined in humans, including intrinsic host factors (e.g., age or genetic), perinatal host factors (e.g., maternal infections during gestation, presence of maternal antibodies), extrinsic factors (e.g., infections, parasites, microbiota), behavioural factors (acute and chronic psychological stress, sleep), nutritional factors, environmental factors or vaccine- and administration-related factors [5]. Vaccination efficacy can be determined based on obtained final results, such as disease prevention, reduction in the clinical course of the disease or immune response [6]. Heininger et al. (2011) observed some issues with the definition of vaccination failure. They, therefore, Afatinib dimaleate divided the causes of this phenomenon into two main groups: vaccine failure and failure to vaccinate. Vaccine failures were further divided into host-related and vaccine-related factors. In pigs, host-related factors involve, e.g., immunodeficiency, suboptimal immune response, immaturity of the immune system, inadequate health status, waning immunity, some immunological interference such as maternally derived immunity (MDI) or some incubating infections [7]. The second mentioned group includes such issues Afatinib dimaleate as low vaccine potency, the imperfect antigenic match between field and vaccine (strain, serotypes, genotypes or antigenic variants), interference with other co-administrated vaccines or some manufacturing problems [6,7]. Within the failure of the vaccine, two subgroups were distinguished [6]. The first one was related to incorrect usages, such as the wrong vaccine dose or administration route, lack of booster, inappropriate storage conditions or vaccine use beyond the expiry date [6,7]. The second one included various program-associated problems such as vaccine availability. == 2. Stress == During life, pigs are exposed to many stressors, such as weaning, social integration (crowding/mixing/isolation), transport, food deprivation, light/dark cycles, novel environments, diseases or temperature issues [8]. It has been documented that cortisol, as well as other neuroendocrine components of the stress reaction, can influence the immune system [9]; for example, pigs with elevated cortisol levels exhibit inhibited proliferation of Afatinib dimaleate lymphocytes to mitogens [10]. Based on these findings, it can be thus assumed that various stressors may impact the efficacy of the porcine vaccination. However, the available data on this subject could be more abundant. The influence of mixing unfamiliar pigs on the specific immune response against the pseudorabies virus (PRV) vaccine has been investigated previously [9]. Afatinib dimaleate The mixing increased agonistic behaviour, cortisol concentration in saliva and catecholamine excretion in urine independent of the pigs gender [9]. However, in mixed gilts, no differences in comparison to control gilts were observed; meanwhile, mixed barrows displayed inhibited post-vaccinal immune response and exacerbated clinical signs following PRV exposure contrary to control barrows [9]. Following vaccine administration, restimulated lymphocyte proliferation, immunoglobulin (Ig) M, interferon (IFN) , and interleukin (IL) 10 responses were documented to be decreased in the group of mixed barrows. Moreover, mixed dominants seemed to be more severely affected than subordinates [9]. Thus, it can be assumed that mixing unfamiliar pigs can suppress the immune response to a viral vaccine and further adversely influence protection against infection [9]. Another team of researchers evaluated the efficacy ofMycoplasma hyopneumoniaevaccination at one of the most stressful moments of the pigs lives, that is, the weaning process [11]. In.