Navigating the difference between killed and modified-live vaccines

Determining a plan of action for a health management program can be daunting in and of itself. It is best to work closely with your veterinarian to develop a strong veterinarian-client-patient-relationship (VCPR) to develop that plan. One question that often arises, should I use killed or modified-live vaccines and what is the difference? Your vet will be able to help you answer the first question, which to use. But, hopefully this article will help you understand the difference.

The purpose of a vaccine is to provide exposure to a non-virulent (non-infective) form of a disease agent BEFORE the animal is exposed to a natural infection. This vaccination causes the animal to develop antibodies and cellular resistance that protect against disease or infection. Viral or bacterial vaccines may be killed or live. Live vaccines contain bacteria or a virus that has been modified (MLV). This means they’ve lost their disease-causing ability (attenuated) or are administered by a route that prevents them from causing clinical disease. Killed vaccines are just what the name says – they’ve been attenuated though a process resulting in their death.

There are some advantages and disadvantages to using either of these products. Described below are some of the factors that need to be considered in choosing a vaccine product.



  • Wide variety of disease protection
  • No risk of reverting to “wild strain”
  • No risk of spread between animals
  • Little risk of abortion
  • More stable in storage
  • No mixing required
  • Good stimulant for colostrum


  • More likely to cause allergic reaction
  • Boosters usually required
  • Slower onset of immunity
  • May not stimulate as strong or long lasting immunity
  • Narrower spectrum of protection
  • Blocking by maternal antibodies in young animals
  • Cost often higher than modified live



  • One dose can provide protection
  • More rapid protection
  • Wider spectrum of protection
  • Less likely to cause allergic reaction
  • Cost usually less than killed


  • Possible reversion to virulent forms
  • Disease problems in immune stressed animals
  • Possible excessive immune response
  • Risk of abortion/infertility if directions not followed
  • Not as susceptible to maternal antibody block
  • Proper handling and mixing is very important

So which is better a killed or MLV? The answer will depend on the targeted pathogen, as well as the nature of the relationship between the calf, pathogen and vaccine. Specific vaccine recommendations should be made by a veterinarian familiar with your operation, your type of cattle and the disease problems they typically experience.


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Posted: December 4, 2018

Category: Agriculture, Livestock

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