Modified Live Vs. Killed Vaccines: Advantages and Disadvantages

The general premise of vaccination, that it presents an animal with an imprint of disease so the immune system can respond more quickly and effectively to the real thing, isn’t complex. However, with the rapid advances in vaccine technology, and broad choice of new and proven product offerings, selecting a vaccine, as well as injection timing appropriate for your operation, certainly can be.

In general, live vaccines introduce a weakened, or modified, live pathogen while killed vaccines introduce a dead pathogen, along with an immune stimulating adjuvant. Both promote production of pathogen-recognizing memory cells without causing actual sickness. Memory cells remain on alert for similar viral or bacterial invaders, ready to mount a protection response when the real pathogen makes an appearance.

Generally, live vaccines result in a faster response, providing effective protection in as few as three to five days, but have been known, occasionally, to cause actual sickness. Killed vaccines are considered safer, but usually require a second dose for full effectiveness. Also, viruses tend to work better in the modified-live form and bacteria as killed vaccines, but this is only the most general introduction. For every generality, there are important exceptions. Technology has added wrinkles to the vaccine equation.

Modern live vaccines are safe and reliable. While certain killed vaccines are now effective with a single dose. Multi-antigen vaccines, containing a range of live and killed, bacterial and viral elements in a single dose, offer advantages for ease of use and animal stress management. The first modified-live bacterial vaccine has even entered the market.

As to which of these products should be part of your animal health program, there are many decision points but no hard and fast rules. In general, a choice of vaccine will be based on the receiving animal’s immune development and overall risk of infection. Will cows be treated before breeding or after? Will calves be vaccinated while still on the cow or during weaning? Will the introduction of outside cattle bring new pathogens into the herd? Any of these factors may push producers in one direction or the other, but be careful not to oversimplify.

Vaccine decisions are part of the overall management plan, and it gets complicated quickly. Consulting with a veterinarian to choose vaccinations as part of a coordinated life cycle health plan is the most effective way to reduce costly treatments and loss of productivity later on. Being familiar with the tools in your animal health toolbox is important, but being open to new thoughts, frequent feedback and planning for progressive herd health is better.

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