I'm in a drug study trial and my CD4 is monitored very closely. If my CD4 drops much more than 10 I'll be out of the study. Should I get a flu shot and how much will the flu shot affect my CD4 or will it?
A vaccination or an illness, such as a viral infection, can transiently cause an increase in the HIV viral load. In most cases, this will resolve with a return to the previous viral load level. It's possible, but unlikely, that these events could cause a significant decrease in the CD4 cell count. More prolonged and sustained elevations in the viral load will cause the CD4 cell count to decline over time.
In addition, a change of 10 CD4 cells, for example from 200 to 190 cells/ml, would NOT constitute a 'significant' decrease in your CD4 cell count, that is, this difference would fall within the range of the variation of the test, and so would not represent a significant clinical change in your CD4 cell count.
More importantly, I would suggest that you should not make this decision on the basis of your inclusion or exclusion from this trial. The best criteria upon which you and your doctor should answer this question is, is the flu vaccination in the best interest of your health?
Unfortunately, there are some settings in the world in which access to antiretroviral therapy can be obtained only be participation in a clinical trial. If this is your circumstance, then I would understand your concern, particularly if exclusion from the trial meant that you would no longer have access to ART. In that unusal circumstance, I would advise you and your doctor to defer the influenza vaccine in order to reduce the already very small chance that the vaccination might contribute to a decrease in your CD4 cell count.
Under most other circumstances, I would advise you, as I advise all of my patients, to have a flu shot, i.e. an influenza vaccination, because the benefits far outweigh the small risks.
I would urge you to take your concern and these observations to your doctor and to the investigator who is conducting the trial, in order to further discuss your options and reach the conclusion that is in the best interest of your health.