| Methods |
Case‐control study to assess influenza vaccine effectiveness among children aged 6 to 23 months within the Northern California Kaiser Permanente Medical Care Program who tested positive for influenza during the years 2003 to 2006 |
| Participants |
Description of cases: children aged 6 to 23 months whose families were enrolled in Kaiser Permanente Northern California membership who tested positive for influenza during the years 2003 to 2006
Description of controls: participants without a positive influenza test were matched to each of these cases based on birth month/year and zip code |
| Interventions |
1 and 2 doses of the trivalent inactivated vaccine against laboratory‐confirmed influenza |
| Outcomes |
|
| Funding Source |
Government |
| Notes |
The authors conclude that “during the 2005–2006 influenza season, when predominant circulating virus strains and vaccine strains were well‐matched, vaccination was 76% (95% CI: 37% to 91%) effective against laboratory‐confirmed infection. There was no statistically significant effect of vaccination, however, for the 2003–2004 or 2004–2005 seasons. Our results highlight the need for further study of influenza vaccine effectiveness in this age group”
A very strangely reported study with Results before Methods (pages are numbered consecutively, though). Unclear case selection process and no mention of blind exposure assessment. No data were available on symptom status of cases or controls. |
| Risk of bias |
| Bias |
Authors' judgement |
Support for judgement |
| CC‐Case Selection |
High risk |
Not clearly described |
| CC‐Control Selection |
Unclear risk |
Apparently same population |
| CC‐Comparability |
High risk |
Insufficient description |
| CC‐Exposure |
Low risk |
Secure record |
| Summary assessments |
High risk |
Lack of information about study design and matching method |
