Hey there Chan! Your letter is very short. I don't think it goes into enough detail about your personal character, duties/ responsibilities, accomplishments/ achievements, competence, experience and skills relating to the health field, etc... Most effective letters are about a page long, I'd say. So I think you really need to go into more details about what you do at this job and how that translates into your want for this graduate program.
to provide comprehensive support services for HIV/AIDS, Tuberculosis, and Blood Transfusion team which I am currently leading.
This whole part is awkward. You provide services for the team? Who are the people you provide services to? Is it agencies? People suffering from HIV and TB? Saying you provide services to the team is just unclear. What kinds of services? Also, you have clearly identified that this person is a boss, you don't need to add the "to which I am currently leading" part.
How do you communicate effectively? What kind of assistance do you provide? Be more specific.
he is apparently in an unofficial leadership role.
This is also awkwardly written. You don't need to say apparently if you feel that you are unofficially a leader and take the lead on projects or give advice, etc...
I would also include more about what you feel your skills and strengths would be that will help you succeed in this program.