SQL Select Distinct on one column--but as it applies to each patient in the select statemtn

Here is my query;

select Name, rx.RowUpdateDateTime, rx.VaccineName, ap.PrimaryCareID from AdmVisits AV
left join PhaRxImmunizationData rx
on AV.VisitID = rx.VisitID
LEFT JOIN AdmProviders ap
ON AV.VisitID = ap.VisitID
where rx.VaccineName is not null and
ap.PrimaryCareID IN (
                                    'PHYSICIAN1', 'PHYSICIAN2', 'PHYSICIAN3', 'PHYSICIAN4'
                              )
order by ServiceDateTime desc


When I run this, I get the following;


Name                                     RowUpdateDateTime                           VaccineName              PrimaryCareID
PATIENT 1                              2016-10-31 22:43                                   Tetanus                        Physican1
PATIENT 1                              2016-10-31 22:42                                   Tetanus                        Physican1
PATIENT 2                              2016-10-30 19:43                                   Pneumococcal            Physican1
PATIENT 2                              2016-10-30 19:43                                   Pneumococcal            Physican1


I can tell the system is updating the immunization twice--probably due to a workflow with the nurse, etc.  I don't really care to have it twice though, I just want a single list of each unique immunization the patient received.  So, I'm stuck on getting that distinct select to work ONLY on the immunization name.  I've tried a variety of group by, etc. with no luck.  Thanks for any help!