 A mild flushing reaction has occurred in about 15% of patients, and more rarely reported side effects include chills, fever, malaise, leukopenia, neutropenia and leukocytosis.Some of these side effects may be attributed to a temporary Herxheimer reaction in response to pathogen die off.According to Hemispherx and patient testimonials, side-effects, when they occur, usually subside within three to four months or less.