Research conducted in mice suggests the food additive tert-butylhydroquinone (tBHQ) — found in many common products from frozen meat to crackers and fried foods — suppresses the immune response the body mounts when fighting the flu. In addition to increasing the severity of flu symptoms, the study found evidence that tBHQ exposure could reduce the effectiveness of the flu vaccine through its effects on T cells, a vital component of the immune system.
Source: Common food additive may weaken defenses against influenza