Vaccines can fail to provide immunity for a variety of reasons, which can be broadly categorized into two main types: Primary and Secondary vaccine failure.
Here are the key factors contributing to each type of vaccine failure:
Primary Vaccine Failure
Primary vaccine failure occurs when an animal’s immune system does not respond to the vaccine as intended, resulting in a lack of protective immunity from the outset.
- Improper Vaccine Storage and Handling: Vaccines need to be stored at specific temperatures. Exposure to temperatures outside the recommended range can reduce the vaccine’s effectiveness.
- Improper Administration: Incorrect administration techniques, such as using the wrong injection site or not following the recommended dosing schedule, can reduce vaccine efficacy.
- Vaccine Composition: Differences in vaccine strains or variations in the manufacturing process can affect the vaccine’s ability to elicit a strong immune response.
- Immune System Status: Immunocompromised animals or those with certain underlying health conditions may have a diminished ability to mount an immune response to the vaccine.
Secondary Vaccine Failure
Secondary vaccine failure occurs when an animal initially responds to the vaccine but the immunity wanes over time, leading to susceptibility to infection.
- Duration of Immunity: Some vaccines do not provide lifelong immunity. Booster doses may be necessary to maintain immunity over time. The duration of immunity can vary based on the type of vaccine and the pathogen it targets.
- Pathogen Variability: Some pathogens, mutate frequently, leading to changes that can render previous vaccinations less effective or ineffective.
- Exposure to High Levels of Pathogen: In some cases, even vaccinated animals can be exposed to a high enough dose of the pathogen that it overwhelms their immune protection.
- Age-Related Factors: The immune response can diminish with age, leading to reduced vaccine efficacy in older animals. Conversely, young animals may not have fully developed immune systems, which can also affect vaccine effectiveness.
- Interference by Maternal Antibodies: In young ones, maternal antibodies transferred during pregnancy or through breastfeeding can interfere with the vaccine’s ability to stimulate the an immune response.
- Concurrent Infections or Illness: Animals being sick or having an ongoing infection at the time of vaccination can interfere with the body’s ability to mount an effective immune response to the vaccine.
Vaccine-Specific Issues
Certain vaccines have unique challenges that can affect their effectiveness:
- Live Attenuated Vaccines: These vaccines contain weakened forms of the pathogen. If not properly weakened, they can cause disease, especially in immunocompromised animals. If too weak, they may not elicit a strong enough immune response.
- Inactivated Vaccines: These vaccines use killed pathogens. They often require multiple doses or adjuvants (substances that enhance the immune response) to be effective.
Other Factors
- Vaccine Coverage: Low vaccination rates in the herds can lead to outbreaks that even vaccinated individuals might not avoid, particularly if herd immunity is not achieved.
- Programmatic Failures: Inefficiencies in vaccination programs/campaigns, such as poor vaccine distribution, lack of awareness, and inadequate veterinary infrastructure, can contribute to vaccine failure.
