| Methods |
Retrospective cohort study of effectiveness of influenza vaccine Data collection from electronic medical records and immunisation registry database Vaccination status was included as a time‐varying variable using a multivariate Cox proportional hazard model to estimate a HR; this was used because patients continued to be vaccinated during the influenza season. Vaccine efficacy was calculated as 1 minus HR. Chronic medical conditions included. |
| Participants |
Children aged 6 to 23 months |
| Interventions |
Vaccine not specified (see 2003 included strains below).
2003 to 2004 season will include A/New Caledonia/20/99‐like (H1N1), A/Moscow/10/99‐like (H3N2), and B/Hong Kong/330/2001‐like viruses. For the A/Moscow/10/99‐like (H3N2) virus, US manufacturers will use the antigenically equivalent A/Panama/2007/99 (H3N2) virus, and for the B/Hong Kong/330/2001‐like virus, they will use either B/Hong Kong/330/01 or the antigenically equivalent virus B/Hong Kong/1434/02. |
| Outcomes |
|
| Funding Source |
Government/industry |
| Notes |
Circulating strain of A (H3N2)
Data collected during peak of influenza activity. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| PCS/RCS‐Selection Exposed cohort |
Low risk |
Selected group, secure record |
| PCS/RCS‐Selection Non Exposed cohort |
Low risk |
Same methods of the exposed cohort |
| PCS/RCS‐Comparability |
High risk |
Insufficient description |
| PCS/RCS‐Assessment of Oucome |
Unclear risk |
Record linkage |
| Summary assessments |
High risk |
Some doubt arises from the real comparability of the cohorts. |
