Abstract:
The benefits of vaccines have been centred on their specific effects on subsequent infections by target
pathogens. Recent studies, however, have opened up new insights into additional effects of vaccines
known as non-specific effects (NSEs) or heterologous effects of vaccines. While several articles have
reviewed epidemiological and immunological evidence for NSEs of vaccines in humans, similar works
on veterinary vaccines are scarce. The objective of this paper was to review the findings of published
studies on NSEs of vaccines developed or repurposed for use in animals. In total 8412 titles were retrieved
from PubMed and CABI databases on the 30th of April 2021. After the final stage of screening, 45 eligible
articles were included in the review. Data from these articles were summarised and presented here. In
general, most of the vaccines studied in the reviewed articles have beneficial NSEs against multiple
pathogens and disease conditions. There were, however, fewe studies reporting detrimental NSEs from
both non-live and live vaccines which is in contrast to the currently existing evidence of beneficial
NSEs of live vaccines and detrimental NSEs of non-live vaccines. This review may be used as a complement
for future review of RCT studies of NSEs of vaccines in animals and provide a useful addition to
the evolving understanding of the NSEs of vaccines.