RANDOMIZED PLACEBO-CONTROLLED CROSSOVER TRIAL ON EFFECT OF INACTIVATED INFLUENZA VACCINE ON PULMONARY-FUNCTION IN ASTHMA

Background Despite current recommendations, many people with asthma do not receive annual vaccination against influenza, partly because of c oncern that vaccine may trigger exacerbations. Colds can trigger exace rbations, which may be mistaken for vaccine-related adverse events. We undertook a double-blind placebo-controlled multicentre crossover stu dy to assess the safety of influenza vaccine in patients with asthma, with allowance for the occurrence of colds. Methods We studied 262 pat ients, aged 18-75 years, who recorded daily peak expiratory flow (PEF) , respiratory symptoms, medication, medical consultations, and hospita l admissions for 2 weeks before the first injection and until 2 weeks after the second injection. Order of injection (vaccine and placebo) w as assigned randomly. There was an interval of 2 weeks between injecti ons. The main outcome measure was an exacerbation of asthma within 72 h of injection (defined as a fall in PEF of >20%). Findings Among 255 participants with paired data, 11 recorded a fall in PEF of more than 20% after vaccine compared with three after placebo (McNemar's test p= 0.06); a fall of more than 30% was recorded by eight after vaccine com pared with none after placebo (binomial test p=0.008). However, when p articipants with colds were excluded, there was no significant differe nce in the numbers with falls of more than 20% between vaccine and pla cebo (six vs three; binomial test p=0.51), although the difference for PEF decreases of more than 30% approached significance (five vs none; binomial test, p=0.06). This association was confined to first-time v accinees. Interpretation Our findings indicate that pulmonary-function abnormalities may occur as a complication of influenza vaccination. H owever, the risk of pulmonary complications is very small and outweigh ted by the benefits of vaccination.