An Equal Opportunity Provider and Employer

VETERINARY SERVICES MEMORANDUM NO. 800.123 

TO: Veterinary Services Leadership Team

Directors, Center for Veterinary Biologics

Biologics Licensees, Permittees, and Applicants

 

FROM: Jack A. Shere

Deputy Administrator

SUBJECT: Coccidiosis Vaccines

I. PURPOSE

This memorandum provides guidance for licensees, permittees, and applicants 

interested in licensing and manufacturing live coccidiosis vaccines for use in poultry.

II. CANCELLATION

Not applicable.

III. BACKGROUND

Coccidia are microscopic, spore-forming, single-celled parasites that cause lesions in 

the intestinal tract of infected domestic poultry. Developmental stages of the parasite 

occur both within the host as well as outside, and include sexual and asexual stages. 

The developmental stages in the host give rise to a microscopic egg, called an oocyst, 

which is passed out in the droppings. Under appropriate temperature and moisture 

conditions, the oocyst develops within 1 to 2 days to form a sporulated oocyst capable 

of infecting other animals to cause coccidiosis. The asexual replicative phase in the 

parasite life cycle causes intestinal lesions. 

Genetic variability in the host can influence susceptibility. Local inflammatory 

responses in the gut contribute to the detrimental alteration of the gut integrity. Studies 

in B-cell immunosuppressed chickens indicate that antibodies are not necessary for 

protective immunity. In the immune host, the parasite enters the gut, but further 

development is prevented or limited. Most evidence indicates that Eimeria elicit 

species-specific immunity that is not cross-protective.

Eimeria acervulina, E. maxima, E. necatrix, and E. tenella are the most common 

species to infect chickens. In the turkey host, E. adenoeides, E. dispersa, 

E. gallopavoris, E. meleagridis, and E. meleagrimitis are most prevalent. In both 

chickens and turkeys, a relationship is observed between coccidiosis and necrotic 

enteritis caused by clostridia species. 

Animal and Plant

Health Inspection

Service

Veterinary Services

1400 Independence

Ave, SW

Washington, DC

20250

for
VETERINARY SERVICES MEMORANDUM NO. 800.123

Page 2

 An Equal Opportunity Provider and Employer

IV. POLICY

A. True Names

1. The True Name of live coccidiosis vaccines is Coccidiosis Vaccine, Live Oocysts.

2. The Eimeria species in the vaccine are indicated on the product labeling and 

described in the Outline of Production.

B. Seed material

1. Eimeria oocysts are usually stored long term using frozen cultures. Strains stored 

in this way should follow the Master Seed concept.

2. In cases where long-term storage of the Eimeria strains is not possible, the 

applicant may use a rolling stock with continuous passage in the host. Applicants 

wishing to maintain rolling stocks should discuss this option with the Center for 

Veterinary Biologics (CVB) early in the prelicense process.

3. If an applicant changes from a rolling stock to a stable Master Seed, then the 

applicant must conduct efficacy studies using vaccine produced at the maximum 

passage from the Master Seed. CVB does not accept use of a combination of the 

Master Seed concept and rolling stock.

4. The applicant should propagate all seeds for use in chickens, including Master 

Seeds, working seeds, and rolling stocks, in Specific Pathogen Free (SPF) 

chickens sourced from the United States and meeting the specifications of 

Veterinary Services Memorandum No. 800.65. The applicant should propagate 

seeds for use in turkeys in healthy turkeys sourced from the United States.

C. Identity testing. The applicant may use several identifying characteristics, as 

applicable, including oocyst size, oocyst appearance, the location and appearance of 

lesions in the host, or a validated PCR-based test.

D. Birds used for manufacture of serials

1. Due to the life cycle of Eimeria, oocysts are produced in chickens or turkeys. To 

produce oocysts for use in live Eimeria vaccines, the applicant may use healthy, 

commercially available chickens or turkeys sourced from the United States. In the 

case of imported vaccines for administration to chickens, the applicant must use 

SPF chickens sourced from the United States. Permittees wishing to manufacture

and import vaccine for use in turkeys should discuss requirements for turkeys 

used to produce oocysts with CVB early in the pre-permitting process.
VETERINARY SERVICES MEMORANDUM NO. 800.123

Page 3

 An Equal Opportunity Provider and Employer

2. CVB does not accept immunosuppression of birds in order to produce oocysts.

E. Safety testing

1. Live poultry vaccines and the Master Seeds used in those products are typically 

tested for safety in the host species using a 10-fold overdose titer. In some 

instances, other excipients in the seed or final product may have a deleterious 

effect on the host. In those cases, the applicant may need to modify the traditional 

overdose study. Applicants should discuss any requested modifications to the 

overdose safety study with CVB prior to initiating any studies.

2. Vaccine strains may induce minor lesions in the host species. If administering

higher levels of oocysts leads to moderate lesions, the applicant must establish a 

maximum acceptable titer for safe use in the final product. This maximum titer

must be included in the Outline of Production.

F. Efficacy testing guidance

1. Coccidia vaccines are tested for efficacy using vaccination-challenge studies in the 

host species. The applicant must include nonvaccinated, challenged birds in the 

study as positive controls.

2. The applicant may use a challenge strain that is the same strain present in the 

vaccine and administer at a titer that will result in severe lesions in unvaccinated 

control groups. Alternatively, the applicant may use a heterologous challenge.

3. Traditional lesion scoring (a scale of 0 to 4) is used for evaluating challenge 

studies (Johnson and Reid, 1970, Experimental Parasitology, 28:30-36 and 

Diseases of Poultry 10th edition, pages 878-883). Lesion scores of 2 or higher are 

considered clinically significant. The applicant cannot use weight gain as a 

primary or standalone outcome in pivotal efficacy studies, but may choose to 

monitor weight gain.

4. Prior to challenge, the applicant may treat positive control birds with coccidiostats 

or ionophores to maintain them free of coccidia until challenge. The applicant 

must describe the use of these agents in the protocol as well as in the final study 

report. Treating vaccinates and controls differently is a deviation from normal 

study design. CVB allows this exception to its efficacy guidance for coccidiosis 

vaccine studies only. 

5. The applicant may not use antibiotics in an efficacy study to control necrotic 

enteritis.
VETERINARY SERVICES MEMORANDUM NO. 800.123

Page 4

 An Equal Opportunity Provider and Employer

G. Sterility testing

1. The applicant may perform sterility testing for products with an oral or spray route 

of administration in accordance with title 9, Code of Federal Regulations (9 

CFR), part 113.27(e) (Detection of extraneous viable bacteria and fungi in live 

vaccine) and 9 CFR 113.30 (Detection of Salmonella contamination).

2. Depending on the manufacturing process and how the oocysts are treated, the 

applicant may be exempt from testing products, according to 9 CFR 113.28

(Detection of mycoplasma contamination), 9 CFR 113.31 (Detection of avian 

lymphoid leukosis), 9 CFR 113.34 (Detection of hemagglutinating viruses), and 

either 9 CFR 113.36 (Detection of pathogens by the chicken inoculation test) or 9 

CFR 113.37 (Detection of pathogens by the chicken embryo inoculation test). 

Applicants requesting any exemption must provide scientific justification for their 

requests. The CVB will not grant an exemption to testing, according to 9 CFR 

113.37, for products for in ovo use. Due to the risk associated with introducing 

foreign animal disease(s), CVB will not grant any exemptions for purity testing of 

imported products.

H. Potency testing

1. The applicant may use vaccination-challenge followed by lesion scoring as an 

in vivo test to assess serial potency. In this case, the applicant formulates serials 

based on the bulk antigen titers to ensure that each serial contains at least the 

minimum titer per dose of each Eimeria species, as determined in the efficacy 

study. The applicant is not allowed to use antibiotics in a vaccination-challenge 

potency assay.

2. The applicant may develop in vitro potency assays, as alternatives to in vivo

assays, if the assays will determine the number of viable sporulated oocysts of 

each coccidia species in the final product.

I. Association with Necrotic Enteritis

1. Literature currently suggests a link between coccidiosis and necrotic enteritis 

caused by clostridia species. Applicants should pay close attention to signs or 

lesions associated with necrotic enteritis when conducting in vivo studies, and 

report any instances of necrotic enteritis.

2. The applicant must describe the use of antibiotics, or other measures to control 

necrotic enteritis, in the field safety study protocol as well as in the final field 

safety study report. If the applicant observes necrotic enteritis in the field safety 

study, the applicant must report it.
VETERINARY SERVICES MEMORANDUM NO. 800.123

Page 5

 An Equal Opportunity Provider and Employer

3. The applicant must report necrotic enteritis occurring in vaccinated flocks as an 

adverse event.

V. IMPLEMENTATION/APPLICABILITY

This guidance applies to live oocyst-based coccidia vaccines for use in poultry licensed after 

issuance of this memorandum.