When a group of animals is exposed to a disease, many, but not all, will become immune and recover (if they do not succumb to the disease). In other words, not all disease outbreaks / exposure result in uniform immunity across the whole group of animals. In order to ensure that the majority of animals are immune to a disease entity, and avoid the necessity for animals becoming ill to achieve this, vaccines have an important role to play in biocontainment. It is important to remember that vaccination is only part of an infectious disease control program and cannot replace the other aspects of biosecurity (see AHI website http://www.animalhealthireland.ie/page.php?id=132 for further details and leaflets available).

It is equally important to remember that vaccination is not 100% effective in preventing disease, and that individual protection from vaccination is variable. In some instances, vaccination does not provide protection against infection but decreases the severity of clinical disease and/or decreases shedding of infectious organisms e.g. salmonella vaccine.

Prevention of disease is usually best achieved by using vaccines well in advance of disease exposure, with many vaccines requiring a primary course of two doses before protection is complete e.g. clostridial vaccines. However, some vaccines may be used in the face of an outbreak to decrease the severity of clinical signs e.g. live IBR marker vaccines. There are also diseases, such as Johne’s disease, against which there are no vaccines licensed for use in Ireland.

Although uncommon, vaccination carries the risk of adverse reactions ranging from mild injection site reactions to severe anaphylactic reactions. The risks of exposure must therefore be carefully weighed against the risks of vaccination. Happily, regulatory authorities and vaccine companies ensure that rigorous standards are applied to ensure vaccines are of consistent quality, safety and efficacy.

Farmers should contact their own veterinary practitioner to discuss the ideal vaccination strategy for their individual situation as each herd carries a different disease risk profile – there is no “One size fits all” approach to vaccine choice.