Influenza: vaccination caused few adverse effects except sore arms

Clinical bottom line (level 1b)

  1. Elderly patients who received an intramuscular injection of influenza vaccine in the arm were more likely to complain of arm pain than patients who received a placebo injection (NNT = 6 at 21 days) .
  2. There was no clear difference in the overall rate of symptoms between the two groups.
Margolis et al: Journal of the American Medical Association 1990; 264: 1139-1141
Expires November 2003

The study

Double-blinded ?concealed randomised cross-over trial without intention-to-treat
Setting: outpatients, medical centre, USA

354 patients (aged mean 71, 96% male) ambulatory outpatients

Excluded if
  • aged < 65
  • not resident in local area
  • no telephone
  • hypersensitivity to eggs or a history of anaphylactic reaction to influenza vaccine


    • Control Group: (n = 354, 336 analysed): placebo vaccination with saline
    Experimental Group: (n = 354, 336 analysed): influenza vaccine 0.5 ml intramuscularly in the deltoid
    After one week, patients had the other vaccination in the opposite arm.
    95% followed for 7 days

    The evidence

    Outcome Time to outcome CEREERRRR
    (95% CI)    		ARR
    (95% CI)    		NNT
    (95% CI)
    one or more symptoms following vaccination weeks 77
    (22.92%)    		 93
    (27.68%)    		 -21%
    (-57% to 7%)    		 -4.76%
    (-11.33% to 1.80%)    		 -21
    (NNT = 55 to infinity;
    NNH = 9 to infinity)
    sore arm weeks 16
    (4.76%)    		 68
    (20.2%)    		 -325%
    (-617% to -152%)    		 -15.48%
    (-20.34% to -10.61%)    		 -6
    (-9 to -5)

    Comments

    1. This nicely done study answered the concern still expressed by many patients: "The last time I got the flu shot, I was sick the following week. It felt like it gave me the flu." The answer, with some caveats, is "No, you will not get flu-like symptoms after this vaccination; but you might catch something else."
    2. No difference in the rate of fever, cough, coryza, fatigue, malaise, myalgia, headache or nausea was noted between the two groups. However the study is too small to exclude any small differences.

    Citation

    1. Margolis KL, Nichol KL, Poland GA, et al: Frequency of adverse reactions to influenza vaccine in the elderly; a randomized, placebo-controlled trial. Journal of the American Medical Association 1990; 264: 1139-1141
    Search Terms: ?
    Contributor: Bob Phillips and Musab Hayatli, November 1999
    Reviewer: Alec Chessman

    Clinical Question.
    Patient elderly
    Intervention or Exposure influenza vaccine
    Comparison placebo vaccine
    Outcome adverse effects