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Modified-live or killed: a crash course in vaccine types

Both modified-live virus vaccines and killed vaccines have been known to stimulate immunity in cattle. Find out which vaccine type is right for your operation.

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Submitted by Boehringer Ingelheim

A sound vaccination protocol lays the groundwork for a healthy herd. Taking time to make sense of vaccine types is an important part of making informed product decisions, and can work to ensure your cattle are in the best position possible to navigate disease challenges.

“Both modified-live virus [MLV] vaccines and killed vaccines [KV] have been known to stimulate immunity in cattle, but there are some key differences between the two,” said John Davidson, DVM, senior associate director of beef professional veterinary services, Boehringer Ingelheim. “It can be beneficial for producers to know about the advantages and limitations associated with each.”

Modified-live virus vaccines

MLV vaccines contain a weakened or attenuated form of a live virus. Because the virus has been altered, it should not cause clinical disease, but will very closely mimic a true infection.

Once the vaccine is administered, the virus will replicate within the animal’s system and create the opportunity for an immune response. Compared to killed vaccines, MLV vaccines generally provide quicker, longer and broader immunity with one dose, since the virus is able to replicate and behave closer to the way it would naturally behave.1

Although MLV vaccines may stimulate a better immune response, there are some other factors to consider. “Modified-live virus vaccines usually have to be reconstituted and may require more attention to detail when it comes to proper use, handling and storage,” explained Dr. Davidson.

Depending on the specific product, an MLV will usually come in two separate vials. The viral component of the vaccine will come lyophilized, meaning it was freeze-dried to preserve potency. To reactivate the virus, the freeze-dried product needs to be reconstituted (mixed) with the approved diluent from the second vial.

“Once MLVs are activated, they need to be kept cold and out of sunlight,” Dr. Davidson said. “The general rule of thumb is that any unused vaccines be discarded one hour after being reconstituted, regardless of refrigeration.”

Killed vaccines

Killed vaccines contain an inactivated, or killed, antigen that is incapable of replicating in the animal’s system. Because the killed virus does not have that opportunity to replicate, killed vaccines usually require a booster dose.

“The killed vaccine requires more viral antigen, or pieces of the virus, to get enough immune system recognition after administration,” confirmed Dr. Davidson. “Because there is more antigen needed, killed vaccines often cost more.”

The additional dose can amount to added cost, and it could mean slower time to immunity. “Generally, it’s about 30 days later that a killed vaccine has to be boosted,” said Dr. Davidson. “The time from initiation of vaccination until we have what we consider to be protective immunity can be longer for killed vaccines.”

Killed vaccines are more stable relative to an MLV, and they do not have to be reconstituted. A producer is able to pull the bottle out, give a single injection, and put it back in the refrigerator until the next time a dose is needed.

Things to consider

“When it comes to building a protocol, you don’t necessarily have to choose between the two types of vaccines,” advised Dr. Davidson. “In fact, there are many producers who choose to incorporate both killed and modified-live virus vaccines in their protocols, and many veterinarians use this approach as well.”

There are many factors involved in finding the right products to best fit the disease challenges facing your cattle. Dr. Davidson recommends the following three things to get started:

1 – Work with a veterinarian.

“The whole point of vaccination is to help animals remain healthy, while minimizing the risk of economically important diseases, and diseases that are relevant in the area where the cattle are being managed,” Dr. Davidson stressed.

Your local veterinarian can help guide this discussion and help uncover which diseases are economically significant and prevalent. Whether you’re talking about parasite management, protecting against viral or bacterial diseases, or even protozoal diseases, working with a veterinarian is the first step.

2 – Have a written herd-health calendar.

Once you have determined which diseases you’re working against, consider a vaccine administration calendar to help with timing. This will ensure that vaccines are given prior to any potential health risks and your cattle are protected.

“I always recommend having a written herd-health calendar,” said Dr. Davidson. “When health activities are written down and visible for those on the farm or ranch to see, we have greater compliance with protocol and more awareness of herd-health events.”

3 – Stay on label.

Different types of vaccines behave differently and will perform differently. Paying attention to the label is extremely important, and will ensure the vaccine is aligned with your expectations. Product labels will also inform you on the correct route of administration and the dose needed.

“Ultimately, whether you choose a killed vaccine, a modified-live, or a combination of the two, the most important thing is that your cattle are vaccinated against performance-robbing pathogens,” concluded Dr. Davidson.



1 Huston CL. Making sense of vaccine types. College of Veterinary Medicine, Mississippi State University 2014. Available at: Accessed March 14, 2022.


©2022 Boehringer Ingelheim Animal Health USA Inc., Duluth, GA. All Rights Reserved. US-BOV-0187-2022-A

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