The vaccine organism may not be similar enough to the disease-causing organism in a particular herd. This could result in the development of an inappropriate immunity. Passive immunity from colostrum may interfere with the animal ' s response to vaccine for up to six months after birth. It is important that vaccines be given at a time in the animal ' s life when good immunity is most likely to develop. Passive immunity in the calf lasts from 3-8 months.
Many vaccines require boosters and most immunity results after the second injection.
The age or time at which a disease is most likely to be seen When the animal is most likely to be able to build immunity free from the affects of stress, poor nutrition and young age. For purposes of discussion, vaccines used to prevent respiratory disease can be classified as killed vaccines or modified live vaccines. No available vaccine is perfect and both have advantages and disadvantages. They use a large amount of organisms and adjuvants to produce a sufficient immune response. The major advantage of killed vaccines is safety .