RB51 vaccine strain for Brucellosis can rarely be shed in milk. Which statement is true?

• A. RB51 can rarely be shed in milk.
• B. RB51 is never shed in milk.
• C. RB51 is always shed in milk.
• D. RB51 is lethal to cattle.

Answer: (A)

RB51 is a live attenuated Brucella vaccine used in cattle, and like other live vaccines, it can be shed by the vaccinated animal. This shedding into milk happens only rarely and usually for a short period after vaccination, not as a common or ongoing event. That’s why the true statement is that RB51 can rarely be shed in milk. It isn’t correct to say it’s never shed or that it’s always shed, and RB51 is not lethal to cattle—the vaccine is designed to be safe and protective. The occasional, limited shedding is the nuance that explains the correct option.