If an adult gains immunity to the rotavirus can they get it again and what are the symptoms?

Yes: There are many serotypes(genetic variations) of the virus so depending on what serotype you were exposed to another serotype can cause reoccurrence of gastroenteritis at a different time. The symptoms of rotavirus are usually significant vomiting, diarrhea and gassiness. The symptoms usually last 5-7 days. There can be transient lactose intolerance. Adults usually do not get as ill as infants.

Rotavirus: Rotavirus is a reoviridae that causes stomach flu, aka gastroenteritis. Symptoms may include watery diarrhea, nausea, vomiting, abdominal pain, fever, decreased appetite, dehydration as well as cough & runny nose. There are many different Rotaviruses, so recurrent infections can occur.