Complex sentence: Vaccination with the flu shot has been shown to boost the immune system and protect against the seasonal flu in some patients with HIV; individuals who have HIV should only get vaccinated with the inactivated influenza vaccine.
Split into simpler sentences: Vaccination with the flu shot has been shown to boost the immune system and protect against the seasonal flu in some patients with HIV. Finally, individuals who have HIV should only get vaccinated with the inactivated influenza vaccine.