Which condition contraindicates live vaccines?

Live vaccines contain live pathogens that have been weakened, so they can stimulate an immune response without causing disease in healthy individuals. However, in certain populations, such as those with compromised immune systems, administering live vaccines can pose significant risks.

HIV infection is known to compromise the immune system, particularly in individuals who are immunocompromised or have low CD4 counts. As a result, these individuals may not be able to handle the live attenuated organisms present in these vaccines, leading to an increased risk of developing the disease that the vaccine is intended to prevent. Therefore, individuals with HIV infection, especially if they are symptomatic or have a low immune response, should generally avoid live vaccines.

The other conditions listed, such as moderate fever or recent antibiotic treatment, do not serve as contraindications for live vaccines. Moderate fever can be a normal response to vaccination and does not necessarily indicate that a live vaccine should be avoided. Recent antibiotic treatment typically doesn't affect the efficacy or safety of live vaccines, as antibiotics do not act on viruses or live vaccine strains in a way that would compromise the vaccine. Past allergic reactions also do not automatically contraindicate live vaccines unless the allergy specifically relates to a component of the vaccine itself.