Chapter 28 Principles of Vaccination

Question 1

What is the primary goal of vaccination in equine medicine?

Answer 1

To control and prevent infectious diseases.

Question 2

Where can guidelines for vaccinating horses in North America be found?

Answer 2

On the American Association of Equine Practitioners (AAEP) website.

Question 3

What is the difference between vaccine efficacy and vaccine effectiveness?

Answer 3

Vaccine efficacy refers to the reduction in disease incidence in a vaccinated group under optimal conditions, while vaccine effectiveness refers to the vaccine’s performance in real-world settings.

Question 4

How is vaccine efficacy usually evaluated in equine medicine?

Answer 4

Through experimental infections of research horses rather than randomized controlled trials (RCTs).

Question 5

What are the limitations of vaccine efficacy studies?

Answer 5

Their results may not accurately reflect vaccine performance under field conditions.

Question 6

What is the principal advantage of vaccine effectiveness studies?

Answer 6

They provide data from real-world settings, which can be more reflective of actual vaccine performance.

Question 7

What is the main limitation of vaccine effectiveness studies?

Answer 7

The presence of many biases that can influence the results.

Question 8

Why is vaccine efficacy generally expected to be higher than vaccine effectiveness?

Answer 8

Because efficacy studies are conducted under strict, controlled conditions.

Question 9

How is vaccine efficacy calculated?

Answer 9

Using the formula: (incidence in unvaccinated - incidence in vaccinated) / incidence in unvaccinated * 100.

Question 10

What formula is used to calculate vaccine efficacy using a risk ratio?

Answer 10

Efficacy = (1 - RR) * 100.

Question 11

How can vaccine effectiveness be evaluated?

Answer 11

Using either cohort or case-control study designs.

Question 12

What is the rationale for evaluating vaccine efficacy and effectiveness?

Answer 12

Evidence of efficacy is required for licensure, and evaluating effectiveness is important for developing better vaccines and informing cost-effectiveness.

Question 13

What are core vaccines according to the AAEP?

Answer 13

Vaccines against tetanus, Eastern and Western equine encephalitis, rabies, and West Nile virus.

Question 14

What is herd immunity?

Answer 14

A phenomenon where vaccination of a significant portion of the population provides protection to the whole herd, including unvaccinated individuals.

Question 15

Why is herd immunity not applicable to diseases like West Nile virus encephalomyelitis?

Answer 15

Because the infection is vector-borne and horses are dead-end hosts.

Question 16

What are the four types of vaccine-associated adverse events defined by the CDC?

Answer 16

Vaccine-induced events, vaccine-potentiated events, programmatic errors, and coincidental events.

Question 17

What are vaccine-induced adverse events?

Answer 17

Events that would not have occurred in the absence of vaccination, attributable to the vaccine’s properties and the individual’s response.

Question 18

What are vaccine-potentiated adverse events?

Answer 18

Events that might have occurred anyway but are precipitated by vaccination.

Question 19

What are programmatic errors in vaccination?

Answer 19

Adverse events due to technical errors in vaccine storage, preparation, handling, or administration.

Question 20

What are coincidental events in vaccination?

Answer 20

Events that happen by chance or due to an underlying illness, not causally associated with vaccination.

Question 21

Why is it challenging to maintain proper vaccine storage conditions for ambulatory veterinarians?

Answer 21

Both excessive heat and freezing can alter vaccines, reducing efficacy and potentially increasing adverse reactions.

Question 22

What systems does the CDC support for vaccine safety data monitoring?

Answer 22

Vaccine Adverse Events Reporting System (VAERS), Vaccine Safety Datalink (VSD), and Clinical Immunization Safety Assessment (CISA).

Question 23

How does the USDA Center for Veterinary Biologics (CVB) administer adverse event reporting for equine vaccines?

Answer 23

Through a voluntary reporting program, though the data collected are sparse and under-representative.

Question 24

What information should veterinarians record to assist with reporting adverse events?

Answer 24

The vaccine manufacturer’s batch and lot numbers, and the site of injection.

Question 25

What is the recommendation for booster vaccine administration regarding injection sites?

Answer 25

Booster vaccines should not be administered at the same site as the initial vaccination.

Question 26

What are localized reactions following vaccination usually attributable to?

Answer 26

Preservatives or adjuvants included in the vaccine, rather than the agent-specific components.

Question 27

Why might combination vaccines have more adverse events than individual vaccines?

Answer 27

Because they include multiple antigens and preservatives, which may increase the likelihood of reactions.

Question 28

What is the impact of maternal antibody interference on foal vaccination?

Answer 28

Maternal antibodies may interfere with the immunogenicity of vaccines, leading to reduced antibody production.

Question 29

Why is vaccination often delayed until foals are six months old?

Answer 29

To avoid maternal antibody interference and ensure a stronger immune response.

Question 30

What is a potential downside of delaying foal vaccination until six months of age?

Answer 30

An ill-defined sub-population of foals may remain vulnerable to infection during a window when maternal antibodies have waned.

Question 31

Why are inactivated vaccines generally preferred during pregnancy?

Answer 31

They are considered safer for the fetus compared to live-organism vaccines.

Question 32

What are the considerations for vaccinating mares during pregnancy?

Answer 32

Vaccination can boost colostral antibodies for foals, but there is a risk of local or systemic reactions and premature delivery.

Question 33

What is the recommendation for vaccinating mares against equine viral arteritis (EVA)?

Answer 33

Vaccination should not be administered during the last 60 days of pregnancy or the first six weeks of a foal’s life.

Question 34

What are the core vaccines recommended by the AAEP?

Answer 34

Vaccines against tetanus toxoid, Eastern and Western equine encephalitis virus, rabies virus, and West Nile virus.

Question 35

Why might risk-based vaccination schedules vary even within the same barn?

Answer 35

Because the risk of exposure differs based on geographical, environmental, and individual characteristics of the horses.

Question 36

What factors should veterinarians consider when designing vaccine protocols?

Answer 36

Geographical region, season, horse’s age, activity level, and specific risks of exposure to infectious diseases.

Question 37

What is the rationale for vaccinating horses more frequently than once annually in regions with active mosquitoes?

Answer 37

To maintain protective antibody levels throughout the mosquito-active season.

Question 38

What is a key gap in knowledge regarding vaccination during pregnancy?

Answer 38

There is limited evidence on the long-term health effects of repeated vaccination of mares during late gestation.

Question 39

What are the potential benefits of vaccinating foals against Rhodococcus equi or equine herpesvirus-1?

Answer 39

Protection primarily through cell-mediated immunity, as humoral responses may be poor markers of protective immunity.

Question 40

What is the impact of non-steroidal anti-inflammatory drugs (NSAIDs) on immune responses to vaccination in horses?

Answer 40

It remains unclear, though some evidence suggests short-term use of low to moderate doses should not impact vaccinal responses.

Question 41

What is the recommended vaccination practice for neonatal foals and geriatric horses?

Answer 41

Special consideration should be given due to their increased risk of infectious disease and potentially less responsive immune systems.

Question 42

What are the key knowledge gaps in equine vaccinology?

Answer 42

Vaccination during pregnancy, maternal antibody interference, the number of vaccines or antigens, and the impact of anti-inflammatory administration for horses with vaccine reactions.

Question 43

Why is it important to follow current literature and AAEP guidelines for vaccination protocols?

Answer 43

Because recommendations may become outdated as new information and vaccine technologies emerge.

Question 44

How can vaccine effectiveness be influenced by storage and administration practices?

Answer 44

Improper storage or dilution can reduce the effectiveness of the vaccine.

Question 45

What is the significance of calculating vaccine effectiveness using odds ratio (OR) from a case-control study?

Answer 45

It helps evaluate vaccine performance in real-world settings where disease cases and controls are representative of the population.

Question 46

What is the impact of herd immunity on the perception of vaccine effectiveness?

Answer 46

High vaccine coverage can lead to most cases occurring among vaccinated horses, creating a paradoxical perception that the vaccine is not effective.

Question 47

What is the role of epidemiological studies in identifying vaccine-associated adverse effects?

Answer 47

They help clarify associations and identify rare adverse reactions that may not be apparent in smaller pre-licensure studies.

Question 48

How does the CDC classify vaccine-associated adverse events by severity?

Answer 48

From mild events like local reactions to severe events like anaphylactic reactions.