There are several general facts and ideas about vaccines which are important in their use. These vaccines can be expected to be safe and effective if used properly. Remember that no vaccine can be expected to protect perfectly but will reduce the frequency and severity of disease. Many combination vaccines are available. Currently, there is no reason to believe that there can be too many parts in combination vaccines so that the response to one part is reduced.
Vaccines sometime appear to fail to protect from disease.
Excess stress may suppress the immune system and hamper the response to vaccines. Excessive exposure to disease-causing organisms can overwhelm immunity. Animals developing disease before vaccination will continue to develop the disease. The vaccine was given before passive immunity from colostrum is gone . Passive immunity lasts for 3-8 months after birth.