A screening test for influenza immunity: preimmunization antibody titers to influenza virus antigens in atopic patients.
Antibody titers to three common strains of influenza virus, including the Swine Flu strain, were determined in 152 patients in an allergy and pediatric allergy practice prior to planned immunization with influenza vaccine. Because allergic patients are considered to be more prone to hypersensitivity reactions than individuals who are non-allergic, it was deemed prudent to screen for patients who might have pre-existing protective levels of antibody to the viruses. A considerable number of the 152 patients were found to have titers of 1:20 or 1:40 to one or more of the three influenza strains, including the Swine Flu strain. The largest percentage of positive antibody levels was found to be to the A-Victoria strain which has recently been most prevalent in the northeastern United States. The lowest numbers of patients with protective antibody levels were for the Swine Flu strain. Nevertheless, the highest titers occurred with patient specimens tested against the Swine Flu strain. Approximately one-quarter of the patients showed significant levels of antibody (1:40 or more) to one or more of the virus antigens and thus were not vaccinated, avoiding the possibility of untoward areactions which habe been observed in some individuals who have been given the vaccine.