The purpose of this study was to obtain evidence clarifying the mechanism whereby acute respiratory infections provoke asthma. On the day following an injection of killed influenza virus vaccine, nine of ten patients with asthma, but none of ten normal subjects, had a significant increase in the airway obstruction produced by a standard aerosol dose of methacholine. The vaccine alone produced no airway obstruction and there was no evidence of atopic allergy to the virus. The most likely explanation for the obscrved results was considered to be an endotoxin-like "toxic" effect of the vaccine. © 1965.
Ouellette, J. J., & Reed, C. E. (1965). Increased response of asthmatic subjects to methacholine after influenza vaccine. Journal of Allergy, 36(6), 558–563. https://doi.org/10.1016/0021-8707(65)90193-0