## 4 Interactions between Vaccine Administration and Gut Microbiome Status
### Gut Dysbiosis and Its Influence on Vaccine Efficacy in Poultry
1** \\ \hline  & & 15 data (sociociolosis vaccination vs. vaccination + C. _havitation_): & \\  & & 0.3 for Chool index, Shannon index, or inverse Simpson index among treatments & \\  & & 1 \(\cdot\) 4 abundance of Rencelroads, financial, and Morgamson genera & \\  & & 1 \(\cdot\) 4 abundance of Rencelroads, financial, and Morgamson genera & \\  & & 1 \(\cdot\) 4 abundance of Rencelroads pertains & \\  & & 2 \(\cdot\) 4 abundance of Rencelroads pertains & \\  & & 3 \(\cdot\) 4 dex: Live coeidosis vaccine (QktRingla & 15 data (Wee credentials vaccination vs. vaccination + republic): \\  & & 4 \(\cdot\) 4. Chool index, Shannon index, or Simpson index & \\  & & 1 \(\cdot\) 4 abundance of Rencelroads pertains & \\ \hline  & & 14 data: Live Newcastle disease virus (NUV) vaccine, & 42 data (only vaccination vs. vaccination + yeast cell wall product inclusion): & \\ White Roman chickens (male) & Strain Le Sage (Shopke V2D0 five engineering Co, 14d, Ongho, Chash), oral gavage & 1 \(\cdot\) average observed species and Chool index & \\  & & 1 \(\cdot\) addor: [PERSON] family, and vice candidates & \\  & & 1 \(\cdot\) abundance of Rencelroads, Ternetkov, and Dosofofofofof  
In response to antibiotic-free production practices, avian pathogenic _E. coli_ vaccination programs are being integrated into commercial poultry management to reduce the prevalence of colibacillosis in flocks [96; 97; 98; 99]. For example, [PERSON] et al. [98] vaccinated Cobb broiler chicks with a commercially available _aroA_-deleted _E. coli_ vaccine and assessed the cecal microbiota. Following vaccination with _E. coli_ at 1 day of age, richness of cecal pouch microbiota was lower than that of the control group at 3, 14, and 25 days of age. This one-time vaccination with the _aroA_-deleted _E. coli_ vaccine also enriched genera like _Lactobacillus_ and _Escherichia_ at 3 days of age, _Streptococcus_ and _Peptoclostridium_ at 14 days of age, and _Subdoligranulum_, _Ruminococcus_, and _Alistipes_ at 25 days of age [98]. To reduce the prevalence of common poultry pathogens, vaccination programs are constantly being developed for commercial poultry flocks [100; 101; 102; 103; 104; 105]. Some of these pathogens may be associated with elevated flock morbidity (_Clostridium perfringens_) while others are more closely associated with human foodborne illnesses (_Campylobacter jejuni_). Along with assessing pathogen reduction and immunological memory, several of these studies have also evaluated flock microbiome status during the vaccination period [104; 105]. For example, [PERSON] et al. [104] evaluated recombinant protein antigens from _Clostridium perfringens_ as vaccine candidates to prevent necrotic enteritis in Ross broiler chicks. Broiler chicks were vaccinated with one of five different candidate protein antigens at 7, 14, and 21 days of life and cecal microbiota were assessed. The abundance of _Bacteroidaceae_, _Lactobacillus_, and _Clostridia_ (unclassified) families were higher in several of the candidate protein antigen immunization groups while _Enterobacteriaceae_ family abundance decreased in other candidate protein antigen groups when compared to the adjuvant control group [104]. Even though the effects of vaccination programs on ceca microbiota status are not completely understood, it is pertinent to note that the increased abundance in the _Lactobacillus_ family observed by [PERSON] et al. [104] differs from the jejun microbiota status of broilers exhibiting subclinical and clinical _C. perfringens_ infections (depressed abundance of the _Lactobacillus_ family) [103]. Additionally, evenness, but not richness, of broilers' cecal microbiota was influenced by the vaccination of several candidate _C. perfringens_ protein antigens [104]. Alternatively, _Campylobacter jejuni_ is a pathogen that is of little concern for poultry health but is a major pathogen associated with human foodborne illnesses. [PERSON] et al.