A randomised intervention study to examine the effect on immunisation coverage of making influenza vaccine available at no cost

N Z Med J. 1997 Feb 28;110(1038):58-60.


Aims: This study aims to assess the effects of two interventions on influenza vaccination coverage: a simple organisational strategy, and making the vaccine available free.

Methods: Sixteen general practitioners in the Auckland region were randomly selected to participate. Patients over 65 years of these general practitioners were randomly allocated to control, letter of invitation for a flu vaccine, or offer of a free flu vaccine. Administration of a flu vaccine for each person in the study was documented in each general practitioner surgery. Vaccine coverage for each of the three groups was measured.

Results: Results were available for 15 of the 16 participating general practitioners, a total of 2791 subjects. Immunisation coverage rates for control, letter of invitation and vaccine at no cost, were 17%, 27% and 45% respectively. Statistical analysis, allowing for the cluster method used to obtain subjects, showed risk ratios of 1.55 and 2.65 for the two interventions, with p values of < 0.00001.

Conclusions: A potential source of bias in this study is underreporting of administration of vaccine to people in group 1. Notwithstanding this potential bias, both interventions were highly effective at increasing the uptake of influenza vaccine in the elderly population. General practitioners should be recommended to routinely invite patients over 65 years to have a flu vaccine. Given the commitment of the Ministry of Health to the vaccination against influenza of people over 65, this study would suggest that serious consideration should be given to making the vaccine available at no cost to this age group.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial

MeSH terms

  • Aged
  • Bias
  • Family Practice
  • Fees, Pharmaceutical
  • Humans
  • Immunization* / economics
  • Immunization* / statistics & numerical data
  • Influenza Vaccines / administration & dosage*
  • Influenza Vaccines / economics
  • Influenza, Human / prevention & control*
  • New Zealand
  • Odds Ratio
  • Vaccination / economics
  • Vaccination / statistics & numerical data


  • Influenza Vaccines