...does HIV viral load rise when I get the flu?

When the flu enters your body, infection-fighting immune cells (your body’s frontline soldiers) are activated to battle the invader. Activated CD4 cells are more prone to HIV infection than resting cells;once infected, they produce more HIV—and your viral load (VL) goes up.But this jump won’t affect your health, and most studies show that VL returns to baseline after a month or so. If you’re on HIV meds, your VL may not bump up at all.

...and when I get a flu shot?

The vaccine—an inactive version of the flu virus—gives your immune system a training exercise at fighting flu, so that it will recognize and defeat the actual thing when necessary. The vax activates your immune system(with its precious CD4 cells), but at a much lower level than a real infection would. So your VL bump is smaller from vaccination than with the real  deal. Get vaxed.