Unchanged bronchial reactivity after killed influenza virus vaccine in adult asthmatics

Polyvalent killed influenza virus vaccine or saline was administered subcutaneously to 27 asthmatics to investigate the effect of influenza vaccine on respiratory function and on airway responsiveness to inhaled histamine. The patients were adults with mild to moderate asthma. Airway resistance (Raw) and intrathoracic gas volume (ITGV) were measured immediately before and 2, 3 and 21 days after vaccine or saline injection. Raw and ITGV values were used to calculate specific airway conductance (SGaw). Bronchial reactivity was expressed as the provocative dose of histamine diphosphate producing a decrease of 40% in SGaw (PD40). Fourteen (87%) of 16 asthmatics who received killed virus vaccine displayed a significant rise in serum antibody level as measured by single radial haemolysis in gel test. No significant alterations in mean Raw, ITGV and SGaw values were observed after viral vaccination. The median PD40 values for histamine also remained unchanged. However, an increased bronchial reactivity was observed in some patients after administration of virus vaccine or saline. Subclinical natural infection or allergen exposure cannot be excluded as possible causes of the increased airway reactivity in these patients. The side-effects of vaccination were minimal and no more harmful than those produced by saline injection. We conclude that the killed influenza virus vaccine used is effective in boosting serum antibody levels and is suitable for adult asthmatics when prophylactic immunisation is indicated.