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Licensed vaccines can afford varying levels of protection. It is important to read and understand product labeling.

Label indications: Data must fully support label indications and accurately reflect the expected performance of the product.

The USDA can grant one of five possible levels-of-protection statements. (Veterinary Services Memorandum No. 800.202; June 14, 2002.) In declining order of level of protection the label claims are:

Prevention of infection: 
This claim may be made only for products able to prevent all colonization or replication of the challenge organism in vaccinated and challenged animals.

Prevention of disease
This claim may be made only for products shown to be highly effective (more than 80% efficacy) in preventing clinical disease in vaccinated and challenged animals. The efficacy must be at least 80% in challenge studies comparing appropriately vaccinated animals with non-vaccinated controls.

Aid in disease prevention:
This claim may be made for products shown to prevent disease in vaccinated and challenged animals by a clinically significant amount which may be less than that required to support a claim of disease prevention (see above).

Aid in disease control: 
This claim may be made for products that have been shown to alleviate disease severity, reduce disease duration, or delay disease onset.

Other claims: 
Products with beneficial effects other than direct disease control, such as the reduction of pathogen shedding, may make such claims if the size of the effect is clinically significant and well supported by the data.