Effect of Short Message Service Reminders in Promoting Seasonal Influenza Vaccination, Western Australia, 2016
| Characteristic | Intervention Groupa | Control Group | Absolute Risk Difference % | RR (95% CI) | NNTb | ||
|---|---|---|---|---|---|---|---|
| Total No. | Vaccinated No. (%) | Total No. | Vaccinated No. (%) | ||||
| Overall | 6,177 | 769 (12.4) | 6,177 | 548 (8.9) | +3.5 | 1.39 (1.26–1.54)c | 29 |
| Age-group, y | |||||||
| <5 | 1,487 | 131 (8.8) | 1,530 | 55 (3.6) | +5.2 | 2.43 (1.79–3.29)c | 19 |
| 5–17 | 380 | 27 (7.1) | 403 | 33 (8.2) | −1.1 | 0.86 (0.53–1.38) | ... |
| 18–64 | 2,478 | 272 (9.5) | 2,463 | 179 (7.3) | +2.2 | 1.31 (1.09–1.58)c | 45 |
| ≥65 | 1,832 | 376 (20.5) | 1,781 | 281 (15.8) | +4.7 | 1.26 (1.10–1.45)c | 21 |
| Indigenous status | |||||||
| Indigenous | 517 | 28 (5.4) | 480 | 22 (4.6) | +0.8 | 1.04 (0.61–1.79) | ... |
| Non-Indigenous | 3,004 | 356 (11.9) | 2,979 | 257 (8.6) | +3.3 | 1.34 (1.16–1.56)c | 30 |
| Sex | |||||||
| Male | 2,921 | 380 (13.0) | 2,927 | 254 (8.7) | +4.3 | 1.47 (1.27–1.71)c | 23 |
| Female | 3,249 | 389 (12.0) | 3,241 | 294 (9.1) | +2.9 | 1.33 (1.15–1.53)c | 35 |
| Preexisting chronic medical conditionsd | |||||||
| Yes | 3,107 | 400 (12.9) | 3,138 | 286 (9.1) | +3.8 | 1.40 (1.22–1.61)c | 26 |
| No | 3,070 | 369 (12.0) | 3,039 | 262 (8.6) | +3.4 | 1.38 (1.19–1.60)c | 29 |
| Pregnancy statuse | |||||||
| Yesf | 115 | 20 (17.4) | 124 | 24 (19.3) | −2.7 | 0.90 (0.53–1.54) | ... |
| No | 747 | 50 (6.7) | 709 | 36 (5.1) | +1.2 | 1.32 (0.87–2.00) | 83 |
| History of influenza vaccination with practice | |||||||
| Yes | 1,998 | 552 (27.6) | 2,011 | 406 (20.2) | +7.4 | 1.33 (1.19–1.48)c | 13 |
| No | 4,179 | 217 (5.2) | 4,166 | 142 (3.4) | +1.8 | 1.53 (1.25–1.89)c | 55 |
NNT=number-needed-to-text.
↵a The treatment group received a short message service message reminding them they were eligible for free influenza vaccine and recommending they schedule an appointment for vaccination; the control group received no such message.
↵b NNT defined as the inverse of the absolute risk difference.
↵c Significant at P <.05.
↵d Chronic medical conditions included asthma, diabetes, chronic lung disease, and chronic heart disease.
↵e Pregnancy was assessed in female reproductive-aged (18–44y) patients only.
↵f Because of small cells and issues with convergence in the model, fixed effects for site were not included in these models.