Why vaccinations fail

With growing concerns regarding antimicrobial resistance (AMR), the saying 'prevention is better than cure' is more relevant than ever.

- Koos du Pisanie

Immunisation plays a crucial role in maintaining livestock health by preventing disease before it occurs. While vaccination may not offer complete protection, it significantly reduces both the severity and frequency of specific diseases.

The effectiveness of a vaccine depends on several factors, including the type of vaccine used, the route of administration, the adjuvant involved, the animal's overall health and condition, and how the vaccine is stored and handled. However, there are exceptions, and this article explores those in the context of particular vaccines and diseases.

In addition to enhancing animal welfare, immunisation serves as a form of insurance – an investment in the long-term productivity of a herd. The protection it offers should be weighed against the potentially devastating impact of a disease outbreak in a naïve herd. Even during challenging times, the cost of vaccination is often far cheaper than the cost of treatment or the loss of a single animal. This raises a critical question: What is the true value of this investment?

Rather than asking whether a vaccine failed, it is better to consider which factors may have compromised its effectiveness. What might have prevented the animal from mounting an adequate immune response? Several factors affect vaccination outcomes.

Timing

If a vaccine is administered during the incubation period of a disease, or shortly before or after the animal is exposed to the pathogen, it may not prevent illness. In such cases, the animal can still become sick despite having been vaccinated.