Which of the following is an example of an oral vaccine?

The correct response identifies adenovirus as an example of an oral vaccine. Oral vaccines are administered through the mouth and are specifically designed to trigger an immune response in the gastrointestinal tract, which is particularly effective for certain pathogens.

The adenovirus vaccine, for instance, is available in an oral form and is used primarily in military settings to protect against respiratory infections caused by adenovirus types 4 and 7.

In contrast, the other options (measles, hepatitis B, and varicella) are typically given via injection rather than orally. The measles vaccine is part of a combination vaccine administered through injection; the hepatitis B vaccine is a series of intramuscular injections; and the varicella vaccine is also given through injection. Understanding the route of administration for vaccines is essential in immunization practices, as it affects how the body responds and builds immunity.