Local and Systemic Antibody Responses in Beef Calves Vaccinated with a Modified-Live Virus Bovine Respiratory Syncytial Virus (BRSV) Vaccine at Birth following BRSV Infection

Abstract

Maternal antibodies interfere with BRSV vaccine responses and efficacy in young calves. The objective of this study was to determine if vaccination before the complete absorption of colostral antibodies results in adequate immune priming and clinical protection of beef calves. Within 6 h of life, calves were randomly assigned to 2 different treatment groups. Group Vacc (n = 25) received a single dose of a modified-live virus (MLV) BRSV vaccine intranasally (IN) and group Control (n = 25) received 2 mL of 0.9% saline IN. At approximately 3 months of age, all calves were experimentally challenged with BRSV. Serum and nasal secretion samples were collected before and after challenge for BRSV real-time RT-PCR and antibody testing. Respiratory signs were not observed before challenge. After challenge, respiratory scores were similar between groups. On the challenge day, >40% of calves in each group were febrile. The mean serum and nasal BRSV-specific antibody titers indicated natural BRSV exposure before the experimental challenge in both groups. All calves tested positive for BRSV and had a similar duration of shedding after challenge. Based on these results, vaccination at birth does not offer advantages for immune priming or clinical protection for beef calves in BRSV-endemic cow-calf herds.

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“…This recommendation contrasts with the findings of Woolums et al (2004), who previously demonstrated the efficacy of intranasal BRSV vaccination in calves, even in those with maternal antibodies. Immunohistochemical analysis conducted by Martínez et al (2023) revealed alterations in T and B cell distribution, with a notable emphasis on lung-associated lymphoid tissues and tonsils, underscoring the importance of local immune responses in their study.…”

“…Due to these considerations, Chamorro and Palomares (2020) do not advocate for the administration of this vaccine in debilitated or stressed animals. Similarly, Martínez et al (2023) propose intranasal BRSV vaccination in calves after one month of age to mitigate interference from maternal immunity and to elicit durable local and systemic immune responses. This recommendation contrasts with the findings of Woolums et al (2004), who previously demonstrated the efficacy of intranasal BRSV vaccination in calves, even in those with maternal antibodies.…”

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“…This is a particular concern for MLVs that could be inhibited by pre-existing immune responses. With respect to young animals, it is the potential for maternal antibodies to interfere with the adaptive immune responses to MLV vaccination [ 77 ]. As the maternal antibodies decline, a potential window of pathogen susceptibility can occur before the vaccines can stimulate adaptive responses.…”

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“…Some intranasal vaccines suffer from interference with maternally derived antibodies (MDA). Martinez et al, showed that modified-live virus (MLV) BRSV vaccines reduced the risk of morbidity in calves with absence of MDA at initial vaccination, but failed to demonstrate significant morbidity reduction when calves were vaccinated in the face of MDA (15).…”

“…In addition, the spaceoccupying effect also reduces the risk of population by other pathogens. This is also of benefit in an outbreak situation, allowing a more rapid immune response without the same demands on the immune system as systemic vaccination (15). Aligned with this benefit, intranasal vaccination can also be used alongside treatments if required, due to the lack of interference with the systemic immune response.…”